It would be good if the three of you could get some therapy. In my state if a couple with children divorces, they must attend 6 sessions of counseling about the children. The subject is how to NOT turn the child against a parent, how to make decisions together and how to insure a peaceful future with the children.
Document everything. Also, know your son has gone through trauma, in a child's mind if mommy can live without daddy maybe she will want ME gone too. However you child behaves make it clear that you love him. Tell him you love him, don't take his actions personally.
Make some clear cut rules for your home (exp. we do homework after dinner, we do not speak disrespectfully, etc, not too many rules). If he says something disrespectful respond with"I respect myself too much to be talked to that way" and walk away. If your son says something daddy said about you, stay calm and say something like, well daddy is sad/angry and sometimes people say mean things when they are sad/angry. Make sure he knows it's okay for him to love his daddy.
If things get way out of control, he may need to talk to a therapist who can help hi through his feelings and help you if you need to change visitation.
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