Hiraeth - Sirius Black x Reader

"The marks humans leave are too often scars."

Young!Sirius Black x Fem!OC
5th year of Hogwarts

Sirius Black - the infamous Gryffindor rebel. Belongs to a racist pureblood family, but has enough nerve to defy the entire concept of blood supremacy. Has amazing and loyal (even Peter, for now) friends.
In a nutshell, everything Ash Green has ever wanted, even though she'll never admit it, even to herself.

Ash Green - the icy stone cold Slytherin bitch. Also belongs to a racist pureblood family, but hasn't yet mustered the courage to defy the only people who "love" her. Has acquaintances, of course, she's a Slytherin. But with selfless friends? She doesn't really have much experience.
In a nutshell, she represents the life Sirius Black denied living.

But is it really that simple? Are they really always gonna hate each other?

This is my first fic, so I really have no idea how to do this. Please don't sue me or whatever.
Disclaimer: The Harry Potter franchise and all its characters belong to JKR (unfortunately, yeah, I don't support her in any sense, lemme make that clear). The OC(s) and my storyline belong to me.

And, also, I hate Snape, so you're gonna get a gist of that. Snape stans, stay away.