imo, he's kinda neutral. He wanted to help Aria, I mean like emotional help, like a friend to cry on. But he also can't do that because of Mielle and his older sister.
It's not really clarified as of chapter 63, but he's not good or evil. It's shown that he at least cares for out mc's wellbeing, so he definitely doesn't have any motives to hurt her, if that's the main thing you're wondering. He's actually not too relevant as of right now.
I’ve read the entire novel so this is distant and away spoilers.
He is kind and he does come to have a crush on Aria but he has no backbone. His sister is the most powerful one in his family and he does what she says, especially after she threatens Aria. Towards the end when he does stand up to his family they lock in up so it comes to nothing, although he does testify against them in the end.
In the first part of the story he’s a tool who teaches Aria that she can handle things on her own and she doesn’t really need a guy to achieve her goals. In the later half he’s a foil for the ML who is someone’s that Aria can actually depend on (although she can take care of most everything herself and helps the ML as much as he helps her).
I’m still in the early chapters So if someone please Can someone explain Oscar to me like is he bad is he good?? What is his deal??