Evil bio, Dad... what do I do?

My fiance's son's biological father is a real knob. He looks for conflict wherever he can find it. If not, he'll create it. We try not to get sucked into his game but he's so good at being a jerk, it's difficult. Before I came along he didn't want anything to do with his son unless my fiance would get back with him... (can you believe this???) I come along two years ago and he was nothing but belligerent. It wasn't until we decided we wanted to move out of state for career reasons that he decided to contest. He pays minimal support and takes little initiative as a parent, but just enough for the court to side with him. We couldn't move... and he makes life here awful. Despite our good will gestures, he only feigns to return them. I'm told all we can do is deal with it. Is there anything at all we can do? I feel like a full-time parent with no rights. He's an "at-will" parent with all the rights. Getting married soon and having a baby. Still feel like I have no say with my own family.