A good guy finally

Okay so I have a bit of a dilemma. I’m sure there are some other ladies who have navigated through this successfully... I’ve always gone for assholes/bad boys/whatever you wanna call it. I finally found a guy who treats me right and we’ve only been dating for a little while. I can feel him pulling away and he says it’s because he doesn’t make me happy. Nothing I can say or do will make him believe that he is everything I want. What can I do or say to prove this to him and stop him from pulling away?