Im curious, ive noticed that in you fics where they're children/teenagers, Sirius and Lily either outright dont get along or are pretty "meh" with each other, but they always get along swimmingly as adults. Is this simply just maturity or is there a deeper reasoning for it?

There's no deeper reason aside from the fact that Sirius, as I write and envision him as a teenager, is fearful of losing the little love and security he has in his life, therefore he doesn't like the idea of James having a girlfriend, especially not one he really likes, because it takes his time and attention away from him. James is the most important person in Sirius's whole world, and as his biological parents didn't exactly raise him in a healthy or emotionally stable environment, if they raised him at all, he's not equipped with the skills to sufficiently manage his emotions and impulses very well, so he reacts by trying to push that girlfriend out of the picture until, inevitably, he realises that he actually quite likes Lily as a person. And it's not just with her, either, in noob he's even worse with Georgia.

Aaaaaaah thank you! Asks like these are my favourites!

The hostility had to stop first, for James's development more than anyone else's. If he still despised Josie, he would feel no guilt about his and Georgia's breakup because he'd be confident in his belief that her fears re: Josie were completely unfounded, and his guilt plays a pretty big part in how things develop.

Have a snippy from 14

"It doesn't matter. It doesn't have to matter. Why do you always smell so good?"

Sucker by the Jonas Brothers is the first one that came to mind. So that's my answer.