3rd person pov
You had always been more 'to yourself' than James. Not a social butterfly in better words. You had never seen people as 'friends', just acquaintances. As a Slytherin, you were told to never associate with Gryffindor's. Not following that rule, you simply became a 'blood traitor'. Which, simply meant you were classified among Sirius Black and your own brother, James Potter. Between classes; your brother; and his close group of friends, you had never come to notice Sirius' little brother...
Regulus pov
I kept to myself, occasionally hanging around Barty and Evan, but I enjoyed the quiet more than anything. I had been this way since I was young. Until I met this 'blood traitor', Y/n Potter, who was in Slytherin with me. I've never spoken directly to her, but my brother has said a few things of her on occasions.
I was just sitting in Potions, listening to the Professor name off partners for the 'project' he wanted to indulge in.
"...and my last group: Y/n Potter and Regulus Black."
I paused for a moment, watching as Y/n say awkwardly in the seat beside my own. She looked a little tense, but then again, who wouldn't be? We'd never even spoken until now...
Y/n pov
Not good, not good, not good...I can't believe the Professor partnered me with someone who probably hates my guts!!!
"Today you will be making Felix Felicis. Whichever group finishes first and does it correctly will got the to keep their potion."
Oh great...I can make this!! But- yknow- I can't reach anything.
"Go get the stuff we need..." Regulus mumbled, seemingly talking to me. Looking up at him, I frowned.
"Can't. 'M too short to reach them." I mumbled back, slightly unamused with the situation.
"Oh." Was all he said before getting up hesitantly and got the few ingredients that we needed. Except one...
"You're missing something, yknow?" I asked softly, not wanting to be offensive.
"...I can't reach it either." He admitted, obviously hesitant to explain that.
I thought for a moment before getting up and going to my brothers' group. He was paired with a Hufflepuff boy, but that wasn't really my concern.
"Brother, can you get some Rue down for us? Neither of us can seem to reach it..."
He looked at me for a short moment but nodded, laughing a little at the revelation of me and Regulus' height 'deficiency'.
Regulus pov
I watched as James and Y/n got the last ingredient, silently glad for them this one time. I had started on the Potion already so she didn't have to do too much work...wait- why do I care?? She's just a 'blood traitor', what does she mean to me? She's my enemy...
"Here!" She chimed, sounding a little bit less tense than earlier. Maybe a bit more on the happy side this time around.
"Oh. Thanks." I mumbled, putting what I needed of the Rue into the potion. Though, I felt a weird tingly sensation in my stomach when our fingers was grazed each others. Unsure of what it was, I attempted to ignore it. Until I saw the small, almost fond looking smile on her face. I wasn't sure why, but seeing that made my cheeks heat up and my hands feel sweaty. It was uncomfortable but I hid it as well as I could.
"We're done, Professor." I stated bluntly, raising my hand a little to get his attention.
3rd person pov
They ended up getting to keep the potion. Regulus gave it to Y/n to use.
"See ya..." Y/n mumbled to him before going off on her way.
Regulus then went to Barty and Evan's dorm, trying to find an explanation to the feelings that were going on in him.
Regulus pov
I pushed open the door to their dorm, yanking it shut behind me.
"I need help." I stated, frowning.
"Yeah, so?" Evan mumbled, unamused.
"You two are going to help me."
"What is it, Reg?" Barty mumbled, sighing dramatically as he leaned back into Evan's arms.
"I got this weird...fluttery? feeling in my stomach today. And- and my face felt hot...and my hands were all sweaty..." I muttered, stuffing my hands deeply into my pockets.
"Oh- around who~?" Barty asked with a smirk, a mysterious glint lighting up his eye. Even Evan was smirking a little bit, his was just softer- sweeter almost.
"Just...some girl."
"She's not just 'some girl' if she makes you feel this way." Barty huffed out.
"Yeah, Reg. This feeling you've got is for speeeecial people." Evan added, causing Barty to nod.
"'Special'?" I mumbled, obviously confused "how so?"
"Reg. Dude." Evan mumbled; looking at Barty, in which he was still snuggled in his arms.
"That right there, is love." Barty finished, looking up at me with a smirk.
"I'm sorry- what?" I hissed, beyond confused. I was slightly annoyed now; how could I like the 'blood traitor', my older brothers' friend?!
"Yeah, you're crushing on someone. This is-" Barty grinned before I cut him off.
"It's terrible! You're telling me the I'm crushing on a Potter??" I snapped, instantly covering my mouth in realization of my words.
"You like Y/n?" Evan mumbled.
"Dude..." Barty whispered, looking between Evan and I.
I huffed and left, slamming the door behind me. Quietly, I mumbled, "I cannot believe I'm crushing on Y/n Potter...wow-"

Bonus scene:

Y/n pov
I climbed out from under Evan's bed and shook my head.
"This is hilarious." Barty grinned.
"...yeah...definitely." I mumbled before carefully sneaking off to my dorm, smiling to myself the whole time.