I am a divorced father with custody. It is not easy for women to accept a man that takes charge of his kids when she has no kids of her own. If a man with no kids dates a woman with kids, he has to adapt to the change if he plans to make it work. Kids comes first. A woman must do that as well. I wouldn't say she should leave him, but instead ask 1) why he must stay at the ex's house to visit and 2) can she become part of the boy's life.

I agree with someone else though, the new woman should not have contact with ex. That is the father's job.