I’m another one asking why you’re putting up with this at all. fessie and company hit it right on the head. You say you don’t want to let the girl break up your relationship, but it isn’t her doing at all; it’s your boyfriend’s behavior that is the true problem, and which doesn’t appear to be headed toward change at all. He is not being a good dad, or even an adequate dad, and that’s the problem, not her.
I don’t want to go around telling people to break up over the Internet, but this is a situation where you are largely powerless unless your boyfriend backs you up. Without that, you’re stuck with minor manipulation, where this girl needs a major intervention in order to wind up with a decent life.