If you are in a relationship that is tearing you up inside then the relationship is not healthy for you and you are denying yourself of your right to actually have a "healthy" relationship.

You can't FIX his resentments he holds onto from his failed relationship. You are not actually in a relationship either, all you are doing is taking up space for a man that needs to work on his OWN issues that he still has from his failed relationship and probably other things that he struggled with in his past as well.