I am wondering what the legal rights are for fathers who pay child support?

The custodial parent is unemployed and an alcoholic, and demands that the father be supervised when he tries to visit, threatening him when he tries to take the child to see his grandparents, etc. It's ridiculous, and he's emotionally very discouraged. What are the steps he should take to make her a more responsible party? She lives with her parents and is milking him financially and emotionally. I don't know that it is best for the child to be with her, but he is hesitant to take her to court and take the child from the mother, as well as feeling generally not up to the challenge of taking full custody. What should he do,and what role should I play as an outsider/girlfriend? I am willing but completely inexperienced with children, and I don't want to traumatize the child but the current situation is making the father miserable and I believe the child may be suffering from things related to her alcoholism and drug abuse.