Is it possible that he might just deny everything you say, call you a liar in front of your son, or somehow try to place all the blame on you during the discussion? It might get really ugly. From the sounds of it, he is trying every way he knows how to not have the discussion. If forced into it, he might try every way he can think of to discredit your decision and feelings in the matter and undermine you in front of your child. Do you think he might do that? Maybe you could get another adult - like a pastor or something like that - to sit in the background to make sure everything stays civil?