Most Helpful Guy
let him go. you are the rebound. this is a slippery emotional slope... if a guy says they "hate their ex" 8x's out of 10 it means he's not over her and actually has some feelings left. He's hurt due to something that happened.
For your part you are in the uneviable position of being the rebound. he is emotionally...let's call it bi polar...right now. He hates her but clearly still likes if not loves her. You are probably going to be pushed away and pulled back as his emotions and feelings fluctuate. him telling you "not to give up on him" is really a selfish act to try and have you but also see where things are and how he feels about his ex