TL;DR  
Sonata is ghey and had a fight with her girlfriend Aria

{Description from the artist}
 
Flash: studying with Twilight So, you’re saying that the square root of the final equation is 12?
 
Twilight: Exactly Flash nods Now, what do we get when we ROUND that number?
 
Flash: trying to think …u-um…I think it’s…ugh! I can’t do this! groans in frustration
 
Twilight: sighs Flash, you KNOW you need to pass this next exam for Algebra, right?
 
Flash: Well..yeah…but this stuff is just too complicate Twilight facedesks Let’s face it, I’m just a brainless moron…
 
Twilight: Hey no, don’t say that pouts, patting his back I’m sure if we just work through pages 35 to the end we’ll get to improving more-
 
Sonata: suddenly rushes into the library WAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHHHHH!!!!
 
in surprise, both Flash and Twilight leap from their chairs
 
Twilight: W-Whoa…S-Sonata? What’s going on? Is something wrong?!
 
Sonata: bawling up crying big time AAAAAAAHHHH, TWILY YOU GOTTA HELP MEEEEE rushes over to them M-Me and Aria just had a HUUUGE fight and Aria won’t even SPEAK to me…not even Adagio can get a hold of her whimpering, buries her face into Flash’s shirt Waaaaaaaaaah I bet she just HATES me NOOOOOW~
 
Flash: flinches when he feels her tears and snot soaking up his shirt Ewwwwwwwwwww……e-er I mean…hey Sonata, i-it’s gonna be alright..warily pats her head in comfort
 
Twilight: U-Um…well Sonata, how did this fight even start? lays a sympathetic hand on Sonata’s back Tell us exactly what happened.
 
Sonata: after bawling and soaking up Flash’s shirt even more, she gets up and wipes her nose …W-Well…i-it all began quite normally. M-Me and Aria were in the hallways, chatting and holding hands like usual. Then we got to teasing eachother, like usual…a-and then I thought it’d end in some little makeouts…like usual…
 
Twilight: Mmhm…go on..taking in the info
 
Sonata: ….sniffling …B-But then the teasing turned into big fighting, and Aria just went and said she hated me! I-I don’t even know why, but she just seemed REALLY angry and….and…bawls again and buries right back into Flash’s shirt WAAAAAAAAAAAH SHE’LL NEVER LOVE ME AGAIN ANYMOOOOOORE sobs some more snot and tears into his shirt
 
Flash: !!! flinches again at the sudden move, trying his best not to cringe
 
Twilight: going over this information, thinks up a solution …Hey Sonata, I wouldn’t be too worried if I were you.
 
Sonata: WHA?? lifts head up again But…WHY? What’ya mean by that???
 
Twilight: Er…well..just think about it. Aria is a very aloof, cold, and keeps to herself alot…right?
 
Sonata: sniffling softly …M-Mhm…t-that’s my Ari alright…
 
Twilight: Right…and from what you said, she doesn’t take kindly to public displays of affection?
 
Sonata: Well…k-kinda, yeah…looking away
 
Twilight: Well then, that’s just it Sonata! She could just be feeling insecure about your relationship, having just started it and all. I know it may not look like much, but perhaps she’s just saying those mean things because she doesn’t wanna bring humiliation on either of you?
 
Sonata: …..H-Huuuuh?
 
Twilight: rolls eyes My point is, just give her some time to think over her feelings more before making such bold moves on her in public. Lots of relationships like this happen, so don’t feel down because she snaps at you for getting too touchy-feely…okay? softly smiles at her
 
Sonata: realizes what this means, her eyes brightening wide ….O M G, you’re RIGHT Twilight. How could I have been SOOO stupid???
 
Flash: looking off to the distance Weeeeeeeeeell-
 
Twilight: narrows her eyes at him Don’t say it.
 
Sonata: ignoring them, as she finally starts to feel better Well, I think I’m gonna go over to my Aria, and try to set things straight for once! Thanks for your help Twilight, those words mean a bunchies to me~
 
Twilight: Hehe, anytime Sonata. Good luck to the two of you.
 
Sonata: Thanks~ nods happily, then turns to Flash And Flash…er…sorry about your shirt*
 
Flash: warily tries to wipe off some of the mess with a napkin …Errr, that’s okay Sonata. You do kinda owe me one for it though chuckles
 
Sonata: Huuuuuh? You mean like THAAAT? her eyes widen, then she cringes EWWWWW Flash, no way! I do NOT swing that way~ shudders in disgust
 
Flash: What? raises brow No, I mean you owe me a new SHIRT, not a date facepalms
 
Sonata: Ohhhhhhhhh, oopsies! Sorry Flash, I was just worried you thought I was one of….“THOSE” girls. I mean, yeah just because we’re SIRENS and like to charm a few guys doesn’t mean we actually LIKE them rolls eyes Besides, I ALWAYS prefer bewbs~ They’re soooo much better~ and soft, and squishy, and sooo round and- >///u///<
 
Twilight: holds up a hand to silence her -T.M.I Sonata….T.M.I

@Wheenesss  
Well, Twilight and Flash were studying each other’s anatomy and Sonata burst in and grabbed the nearest cuddly thing to bawl about her problems.

@Wheenesss
 
Headcanon

How the fuck did this even happen?

I like the artist’s description in the source XD