The pic above is a screenshot I took myself I'm so proud of it. It was/is a beautiful scene I know.
I cried cuz it was too much.
This is written when not many people knew about Alec's relationship
Smut Warning

Alec's blood was pounding in his ears as he feverishly kissed Magnus in his room at the Institute. Even though he knew he was risking everything by letting him in through his window, Magnus usually put a soundproof charm on the door so nothing would be heard.

Magnus kissed him back with passion, his hands flying to his shirt and discarding it quickly and efficiently. Not breaking the kiss, the two removed their clothing and threw them aside. Magnus lightly pushed Alec onto the bed, and pounced, kissing his neck roughly causing Alec to gasp with pleasure. Since Alec knew that there was a charm on the door, he allowed Magnus to do what he wanted to him without hesitation.
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Jace could not fall asleep. As he lay awake in bed, he thought about maybe going to Alec's room to talk. Surely he wasn't asleep already? He usually read at this hour, and woke up in the morning still clutching his book. As he swung his legs over on to the side of the bed, he stopped. He heard something. Putting his ear against the wall he listened closely.

Sounds. Sounds coming from his parabatai's room. As he reached over for a dagger instinctively, he soon realized they were not just any noises.

They were moans.

Jace blinked as he struggled to make sense of the situation. Did Alec have a girl in there? Or a guy? His thoughts wandered mindlessly. Getting up to investigate, he made his way towards his blood brothers room.
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As Magnus slammed into Alec, he moaned exceptionally loudly. Magnus, pleased at his reaction, turned himself a bit and slammed again, this time hitting home. Alec cried out in pleasure, and Magnus continued to thrust into him. At the same time he was pumping Alec, and he could feel Alec getting harder at the minute. He snapped his wrist in an unexpected way around his length, causing Alec to whine. He grinned at this, and continued his handiwork before there was a loud crash, and the two looked up to see that Jace had broken through the door.

Horrified, the three of them stared at each other. Alec seemed frozen, as he knew he aught to push Magnus off or cover up, he found he couldn't even move a finger. His mouth hung open in a gaping O and out of the corner of his eye he saw Magnus blanching, for the first time in his life. Jace's expression looked as if it were a mixture of horror and something else. Finally, when the earth seemed to rotate again, Magnus leapt off of him, magicked some clothes on and Alec pulled the covers on his bed up high. Surprisingly enough, it was Jace who broke the silence.

  "I um, heard some noises and thought you were under attack" he said sheepishly. Alec and Magnus exchanged worried glances. They had forgotten to put the charm on. If Jace had heard, there was a possibility that the others might have too. Alec gulped.

"So sorry you had to find out about our relationship this way, really makes a bad impression on the future in laws" said Magnus, trying to lighten the mood. Alec glared at him before hastily slumping further into the covers.

Jace raised an eyebrow. "Relationship?" he asked, already slightly aware of the answer.

  "What, you didn't think I barged in here and raped him did you?" asked Magnus incredulously. Alec gave him a sour look. Jace looked mortified.

  "N-no of c-course not" he stuttered.
This time Alec raised an eyebrow. Jace Wayland (remember this is before the herondale and everything) was stuttering? Never in a million years. Until today.

"Quiet down guys, the others might here" hissed Alec. Jace stood in the doorway, stick still. Then he raised an arm and pointed at the two.

"So you two are together" he said slowly.

"Pointing out the obvious are you?"
said Magnus sarcastically. Jace and Alec glared at him.

"Hmm. Well big brother I won't tell anyone if you don't want, but I'll never let you live this down. Alec's not a virgin! Alec's not a virgin!" he started to sing, prancing around in circles. Magnus snapped his fingers, and this time no sound came out of Jace's mouth. He silently put his hand over his mouth, then when looking at Magnus's and Alec's smug faces, he realized what had happened. He middle fingered the two before walking out of the door.

"Well, I shall fix the door and put a charm on it. Then we can continue" smirked Magnus. Alec's eyebrows shot up in shock.

  "Even after ALL that just happened, you STILL want to continue!? My brother knows what we're doing in here, and I don't exactly like the thought of that" he whisper yelled. Magnus crossed his arms.

  "You have to finish what you started Alexander, weren't you the one that said you never ran away from an unfinished project?" said Magnus. Alec opened his mouth to protest, but he didn't know what to say. "That's what I thought" laughed Magnus, before fixing the door, locking it, and putting the charm on it.
"You should just be that it was Jace that broke the door, and not Max" he said, before sliding onto Alec and finishing what they had started.

FIN

CAN WE JUST TALK ABOUT THE KISS PLEASE?! TOO MUCH FOR THIS FANGIRL TO HANDLE. I've watched it over what idk 30 times now, still die every time. Ughhhh soooooo perfect. And I added the song to my playlist. Too good! Please vote and comment, Bai my moo moos