Based off of the song above. Back to basic songs ;) also, frisk is an adult and a girl here. Forgot mettaton's gender so I'll mention them as a they.
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Your pov

The audience cheered as you went up the stage. You sat on the small stool in front of the piano as the crowd silenced. You sighed and pressed the keys, eyes scanning the crowd as you sung.

"Wise men say, only fools rush in..."

You saw sans and frisk in the crowd, smiling happily at each other. You smiled bitterly as your heart shattered.

"But I can't help... Falling in love with you..."

You sighed dreamily as you closed your eyes, gliding your fingers on the piano.

Flashback

"Can (shall) I please stay (?) here for today?" You asked sans. He nodded. "sure kid." He smiled at you. "you could stay anytime."

"Would it be a sin?"

You wondered jokingly, preparing a plan to prank sans back.

"If I can't help, falling in love with you?"

You erased the line in the heart shaped red card. You were about to give it to sans because it was Valentine's day but he probably won't like you back.

And you were right....

"Like a river flows.... Surely to the sea...."

You smiled at the scene. "Wow sans. Thanks for taking me here!" He looked at you as you stared into the beautiful clean river. "no prob kid."

Flashback end

"Darling so it goes..."

You looked at the happy couple with dread.

"Some things.... Are(n't) meant to be...."

You thought bitterly as you looked down at the piano, focusing on your performance while holding your tears back.

"Take my hand..."

Flashback...

You took sans' hand as he helped you up when the bullies pushed you.

"Take my whole life too..."

You stared at sans' eyes as you blushed. "Thanks." He smiled at you and went off, going to frisk.

"For I can't help, falling in love with you..."

You stared at them, smiling. "Maybe he doesn't love me back but, at least he's happy..." You stared at your feet, bittersweet tears collecting in your eyes. You put a hand on your chest as your heart ached.

"Like a river flows... Surely to the sea..."

You saw sans and frisk on the river that he took you months ago. They were both blushing at the sight of each other.

"Darling so it goes..."

You gasped as you heard sans confess his love to her. You covered your mouth.

"Some things... Are meant to be..."

They hugged each other as you cried behind a rock. "I guess I'm too late..." You ran away.

Flashback end

You slowed the pressing of the keys in the piano for the song's end.

"Take... My hand..."

Your eyes went back to the crowd.

"Take my whole life too..."

They still stood there, huddled close to each other as they watched you, as if they were teasing you.

"For I can't help falling in love with you..."

You knew they weren't but it felt like it. They both leaned in as your eyes widened.

"For I can't help..."

You just watched as they kissed each other. You felt the pain rise to your throat.

"Falling in love.... With..."

You looked away, clearly not wanting the audience to see that you were crying and choking on petals.

"You..."

Your voice almost cracked as your hands leave the piano. The crowd clapped and cheered as you tried to make the tears unnoticeable and bowed as the curtains closed. You covered your mouth and tried to stop the petals from falling. You went backstage and saw mettaton looking for you. When he saw you, he was shocked as he ran. "What happened to you darling?" You coughed and coughed as the bloody petals went down as well as the tears. Mettaton was your friend and the were the only one who knew about your crush and.... Disease.... "I am so sorry... Were they there?" You nodded as you hugged them for comfort. They tried to calm you down. Your eyes widened as you saw them coming towards you two. Mettaton saw your shocked expression and turned around only to glare in fury. They both stopped once they were beside you. They gasped as frisk tried to come closer. "(Y/n)! What happened?" She tried to hug you but you suddenly pushed her. She stumbled but sans caught her. You froze once you saw the anger in sans' eyes. "what the heck is wrong with you?! can't you see she's just trying to help?!" Your tears became more frequent as mettaton stood up for you. "No she isn't! She's actually making matters worse!" Frisk was shocked and also confused. She was completely oblivious to what she did. "oh really? trying to comfort someone is making it worse? go to school toaster head!" You cried and ran off as they fought. You coughed as the petals made a path behind you. Where were you going? That is unbeknownst to you but you didn't care.

Mettaton's pov

I growled and continued the argument when frisk decided to shout. "Guys! (Y/n)'s gone!" I stopped and looked to my right. She was gone. All that was left were some bloody petals. "well that's great. come on frisk, let's go." I grabbed the bonehead's hood. "Not so fast! You started this, your going to fix it!" "i started it?!" "Sans!" Frisk shouted. "Let's help to find (y/n) alright?" Sans huffed. "fine!" I sighed sadly. Where could she have gone? "Come on, let's follow the petals."

The petals lead us to a flowery field. It was really hard to follow her from there since there were a lot of flowers but we tried. I saw her in the distance and ran towards her. "(Y/n)!"

Your pov

You heard mettaton call out to you. You wiped the tears from your eyes as your throat still burned. You looked as saw the three of them there. You didn't care now. Let them take you. You will die in a couple of months anyways... Mettaton sat beside you. "Come on now. Let's go." He helped you sit up as you walked, well, get dragged, towards the other two. You looked at sans only to get a glare in response. You looked away, tears still streaming in your face as you cough out more petals.

You waited in the waiting room as sans, frisk, mettaton and alphys discuss about your disease and they were trying to find a cure. You coughed and coughed. Man, love really hurts. After a few minutes, the door opened as the four came out. The monster-human couple looked sad and guilty. You avoided each other's gazes as you focused on what alphys was about to say. "S-so, we did f-f-find a solution but i-it come with a p-price." You raised a brow, curious. "W-well. W-we can perform a s-surgery b-but it will m-make you lose y-your feelings f-for him ." Your breath hitched. What? You shook your head. "Sorry alphys but no. I'd rather die than not love him." You murmured, looked away and wiped your tears. You then saw mettaton sit next to you. "Darling. Your my friend and I want the best for you. You really have to agree to this surgery." You shook your head. "Even though sans didn't accept me, I will still love him..." You mumbled but mettaton seems to hear it. They sighed. "Alright, we can make more research about this but if we don't find anything, then we have to perform surgery on you." You sighed. "Fine..." You said while looking at the two in the corner, comforting and talking to each other. You coughed put more petals. You put a hand on your chest. It's getting harder to breathe...

Sans' pov

I just watched as mettaton comforted (y/n). I feel so bad now. I wanted to be there for her but it will only make matters worse. I also love frisk and I can't just leave her! I sighed. Man, this is going to be tougher than I thought. I saw frisk looking at the ground guiltily. I walked over to her and placed a hand on her shoulder. "hey. it's alright. it's not your fault, you didn't know..." She looked at me. "But I should really expected it. I saw how close she is to you, heck I even saw her staring at you, spaced out while you weren't looking." She was right. I sometimes caught (y/n) staring at me but thought nothing about it since I'm so focused on trying to create a plan on how to confess to frisk. I can just imagine how painful that is. Seeing your crush loving another person... Then I thought I was the 'hero' here but guess not. I sighed. Frisk looked at me, worried. I looked to the side. How do I solve this? My feelings were all mixed up. I don't know what to think or say... I just think of her as a friend...

But deep inside, I know that she is worth so much more to me...

Timeskip

Your pov

The coughing just got worse as more petals and blood went out. You can barely even breathe. Mettaton and alphys was always there for you. The others visited you and gave you gifts. Sans and frisk visited you too but not that frequently. Sans didn't really talk much and he has been avoiding you. That just made the feeling worse. So far, you guys haven't found another cure. The first cure, making the other fall in love with you, is pretty much impossible while the surgery is still available. Right now, mettaton was convincing you to take the surgery.

"Come on darling. You don't have much time. You should really accept it." You didn't respond and just looked down, eventually coughing. They are right. You only have 3 days left according to alphys' calculations. You were really tempted to take it but at the same time, you don't want to. You closed your eyes and sighed. Time to make a decision.

Route 1:

"I'll take it." You muttered, still a bit sad. You didn't really want to but you might as well leave them. They shouldn't really worry about you because they have a relationship to worry about. Mettaton smiled. "Well then, what are we waiting for?" You stood up and took you both took your coats from the rack. You coughed and coughed. Mettaton pat your back as you both go into their car. You got into the front seat and stared out the window, eventually coughing out bloody petals. The car started moving as mettaton threw glances at you, worried. Your breaths were shallow and choppy. They drove faster and after a few more minutes, you made it. Mettaton assisted you in getting in the lab. In there, you saw sans and alphys talking. Said skeleton was shocked when he saw you. Alphys turned to you. "o-oh! (Y-y/n)! Mettaton! I didn't e-expect you guys to c-come here!" Mettaton spoke up. "Well, we're here to get that surgery." Sans looked at you, shocked. You avoided his gaze and focused on the other two. Alphys looked shocked and a bit scared but nodded anyways. They both leaded you into the room. You heard another set of footsteps, meaning that sans is coming with. Soon enough, the operation started.

You groaned and opened your eyes, having to squint a little because of the bright lighting that's in the room. You blinked a few times and opened your eyes fully, seeing that your in a hospital like room. Your body felt a little numb, especially on the chest area. You saw that a tube that leads to an oxygen tank was connected to you to help you breath as well as some other tubes that connect to different things. You heard the occasional beep of the heart monitor. You felt a little dull. Like, a part of your emotions was taken out. Well, that's most likely the case. You breathed in and out, relieved that the flowers have stopped. You weren't really used to in taking that much air though so you didn't inhale too deeply. You just waited and stared at the door until it opened. You saw a small team, mettaton, alphys, frisk and sans, come in the room. They looked at you, relieved. You noticed that frisk and sans seems to be avoiding each other. Why though? Frisk smiled. "I guess the operation was a success." Alphys looked at you curiously. "S-so, how d-do y-you feel, (y-y/n)?" You met her gaze. "I feel dull. It's most likely because one of my feelings have been removed." You replied, still thinking that it is quite a weird feeling. Sans stared at you with an unreadable expression on his face. Mettaton sat on the bed next to you and talked, as well as the other two. The rest of the squad came in a bit later and talked but, one thing you couldn't ignore was sans' regretful glances.

Timeskip

No one's pov

Time passed by rather quickly. Your feelings for sans have been removed. You were a bit saddened by it but at least he's happy, or so you thought...

Sans was regretting his choice. He just realized how much he loved you instead of frisk. They broke up when the operation took place but nobody told you. That is why he is talking to alphys. Alphys comforted him since sans didn't want to disturb Papyrus and undyne's once in a lifetime hangout and alphys was one of the friends he relied on. He couldn't go to you since he figured that he would make your condition worse. He also realized that he mistook friendship for love. He made his decision too quickly. Frisk had found her true soul mate a few months later as they lived happily. Sans felt ignored and rejected by you. He chuckled as he looked down at the ground. He was currently in his house, on the couch. You and papyrus were in his room, solving some puzzles together. You didn't really pay that much attention to him, probably afraid of falling in love again. Sans chuckled darkly.

"i guess this is what she felt when I was together with frisk..."

Route 2:

"No..." You said, looking to the side and coughing more petals. Mettaton sighed. "I guess I can't really change your mind, can I?" You shook your head and looked up to the ceiling, a soft and genuine smile on your face.

2 days have passed and you were literally coughing non-stop. You we're currently hanging out with sans when you found out that he broke up with frisk. You were trying to comfort him. You gave him a stern yet soft smile. "Sans, can you promise me something real quick?" You said, barely coughing. Sans was surprised. "i usually hate promises but i guess it's the only way to make it up to you so sure." You looked at him straight in the eyes....errr..... Eyesockets...? Anyways! "I want you to promise me that when I die, can you please burry me close to the river that you bought me to in the past? That place is the place where I fell in love with you..." You mumbled the last few words. That's why that place is so special to you because, as you said, when you went there, that's when you fell in love with sans. His cheeks were dusted blue as he looked away from you, seemingly flustered. His blush then faded as his eye lights flickered a little. He looks like he was thinking of something bad. You coughed weakly. Sans seems to notice it. You looked at him with an expression that tells him to take you now. He sighed and grabbed your hand, teleporting there. He helped you stand up. You coughed violently but you managed to sit down. Some of the petals got into the river as it flowed. You watched them, your eyes half lidded. Sans looked at you, worried. You leaned against his shoulder and coughed, your eyes closing and your breathing was short and ragged. Sans widned his eye scokets. Was he really going to experience you to die right before his very eyesockets? He needed to think fast.

Sans quickly pulled you towards him as you got pulled into a passionate kiss. Your eyes shot open, shocked. You kiss back, albeit weakly. The kiss didn't last long before you fainted. Sans was alarmed. Was he too late? He checked your pulse and sighed in relief. Your pulse was still there but it was faint and weak. He teleported to alphys' lab and alphys scurried over, hearing him call her name. Soon enough, you were put on a bed, tube-like wires connecting to you. The heart monitor's beeps were slow. Sans sat beside the bed you were on, thanking himself for saving you. Alphys walked over to him, her tail dragging across the floor. "H-how did you s-save her s-sans?" She asked. Sans looked away, a blush covering his features. Alphys gave him a knowing look. She failed from holding back a mischievous smirk. "Ooooh~ I know what you did." She giggled. She might've failed from holding back a smirk but she didn't fail on holding back a squeal. She didn't want to disturb you. Sans' blush darkened as his grin widened a little. He put a hand over it. He felt embarrassed but he also felt like a giddy little school girl when she got accepted by her crush. Alphys excused herself and went to her kitchen. Sans heard muffled squeals from there. He took a few deep breaths, trying to cool down. His blush eventually died down as he sighed. He then waited.

Timeskip

6 years have passed since that incident. It took you a year to wake up and sans was so relieved that you actually woke up. You were back to your old self. During the years, you and sans have been together. You were still a bit regretful since you made sans and frisk break up because of you but they said that it was fine and they were happier with their new relationships. Right now, you were with mettaton, performing on stage. Unfortunately, sans can't go to this performance. He said that he had to run some errands but you weren't that upset. You were sure that it's important since sans always takes the opportunity watching your performances so the errand must be urgent. You played some of the instruments while they sung. The crowd was going crazy, clearly enjoying and getting mesmerized by the melody you two produced on stage.

After the performance. Mettaton threw you a wink. "Before we get out of stage, I welcome a special guest to get on stage!" You looked at mettaton, confused. You didn't know about this! He just smirked at you as the crowd clapped. He went back stage and signalled you to stay there. You stood still, not knowing what was in store for you. Then, the curtains opened and in comes.... Sans....? You looked at him, highly confused. "Sans? I thought you won't be able to make it?" You said, moving the mic from your mouth. He looked at you, a light blush dusting his cheeks as he sheepishly smiled. He went beside you and looked at you. He sighed, seemingly nervous. "(y/n)... we have been in this relationship for years now and i thought that we are ready to take a step further. we have been together in almost all our moments..... moments of happiness and sadness... we have been together in solving our problems and celebrating our success..." Is this you think it is? "and.... well..... ah screw it... what i'm trying to say is..." He got down on one knee. You could only watch, frozen. Your face was hot while your mouth was slightly agape in shock. "w-will you marry me?" He took out a blue box and opened it. There was a silver ring with a few shiny gems on it. There was also something engraved on it but you can't really read it. The crowd gasped in shock. Hot, happy tears rolled down your cheek as sans looked away, seemingly ready for possible rejection while also anticipating for acceptance. He flinched as he felt two arms embrace him as well as liquid on the back of his jacket. He heard a faint whisper. "Y-yes..." Sans hugged back. The crowd cheered, a few squeals and whistles being heard. You both let go as sans slipped the ring on your finger. Sans put the box back in his pocket as you both stood up. The cheers grew louder as you held his cheek and stared deep into his eyesockets. Sans took your hand and placed it back down. "not here..." He whispered, a bit embarrassed. The crowd groaned in disappointment but was happy for you both nonetheless. The curtains closed as you both went backstage, hand in hand. Mettaton wiggled their eyebrows at you. "So, how was it darlings?" You smiled, looking away. "I-it was... Something..." "it's memorable i guess..." You both answered. "Well, when's the wedding?"

After being bombarded with questions that mettaton asked, as well as the group when they came, you both went home peacefully. You went to your shared room and changed into comfortable clothes and went back down. You sat beside sans in the couch as he put an arm around your shoulder. He then pulled you down with him as he laid down, you on top of him. You blushed, heart beating fast due to shock. He chuckled at your expression. You blushed and hid your face on his chest. He played with your hair as your blush subsided. You both watched the the in silence. Well, until you broke it. "When IS the wedding?" You asked him. He didn't really answer earlier so you wanted to know. He shrugged and sheepishly smiled. "i didn't really think of that soooo..." You chuckled and tried to look at him with a straight face but failed. "Really sans?" His cheekbones were tainted blue. "Well, I guess we have to plan it now." He groaned. "do we have to do it now?" You were about to respond but he gave you adorable puppy dog eyes. How did he make it? You don't know but you gave in. You sighed. "Fine, we'll plan it tomorrow." He smiled and hugged you closer. You shook your head and smiled. He really likes his cuddles, does he? You then spent the day cuddling on the couch, watching movies and such.

Yeah, I don't really know what else to write so, proposal it is I guess ^_^'''. Also, bad news, I lost most of the requests ;-; . I'll have to do the remaining requests. Don't worry, I'll try to find the other requests. To prevent this from happening again, I'll post a chapter at the start of the book shortly after posting this one. Don't request anything outside of that chapter or I won't accept it. Anyways, bye potato chips! :3