My stepbrother hates me?

He's jealous because he feels like you replaced him. He is adopted, you are your father's son by blood. He feels bad about not being a natural member of the family and so wants to make you feel as bad as he does. I think you should avoid him where possible but when you do cross paths be nice. It's hard to keep hating someone who is nothing but nice to you. You could also tell your dad if he's trying to beat you up but that would be a last resort. No need to be 'carrying tales' on top of everything else. Good luck.