The Good Father (1985)

Bill is a man who's very bitter about his divorce and losing custody of his son. So, when one of his friends is being sued for divorce by his wife so that she can enter a lesbian relationship, Bill decides to help his friend gain custody of his son...in any way that they can devise, including using a sleazeball lawyer. But while Bill feels that feminism has robbed him of his family, he begins to be appalled at what he and Roger have done.