Playing devil's advocate here....as far as your XH is concerned, anyone he considers important to him is family and that would include OW. Of course, in his view OW is not an OW any longer, she is his GF, and a long term one at that. He wouldn't see anything disrespectful in involving a woman who holds an important spot in his life in your S's life.
I know that isn't what you want to hear, but it's the truth of D. You can't expect him to follow your expectations for your S. He will do what he feels is best in his own situation just as you will.
T19 M15 S19 XH47 M43 bomb12/4/07 PA5/07 S12/26/07 D final 11/17/08 Back together with no defined R 05/2010 confused....to say the least!!!