Ex-Wife/ BabyMom making Our relationship difficult.

Ok..I've been dating my current boyfriend for over 5 years. I do not have any children but he does, a daughter who is 15. Being that the Ex-Wife dispises her Ex-husband she makes it extrmely difficult for my boyfriend to see his daughter, not based on any valid reason but only that she doesnt like him. She also put him on child support when the girl was born. After 15 years, this lady has made it so difficult for my boyfriend that he becomes depressed saying that he's a worthless dad even when I can clearly see that he is not. This lady has gone as far as a putting a restraining order against him and even his mother to keep them from seeing this child. If she notices even a bit of happiness from my boyfriend she will try and knock him down so he'll feel worthless again out of spite. She lets the daughter visit her grandmother (BF mom) witht the restraining order but if she feel that my boyfriend or his mother give her attitutude she would call the cops just to see him get in trouble. If Im around..its even worse, the girl will not come over to visit at all. I feel awful that my boyfriend has to go through this and sad that he isnt being given the chance to be the great dad I know he can be...its starting to affect our relationship because he gets so depressed he doesnt want to do anything at all. Is there anything I can do to help him?

Updates
Ok, while I have been with him I have figured out bits and pieced them together...lets just say my BF never physically threatened his daughter but he did end up cheating on his BM while she was pregnant....out of spite and to basically get back at him for what he did she basically refused to let him see his daughter...through all this my BF threatened his BM to let him see his daughter and that she was a profanity for using his daughter to spite him. When his daughter was 5 she told the child to tell the courts that daddy was scary and that she was afraid of him, of course not knowing better the child did and the restrainig order was passed. The girl is now 15 and rebels against her mom alot to try and see her dad, we have invited to girl on outings with us but the BM always makes excuses and tries to keep her busy, like helping her do laundry or taking care of her other child with another ex.