Wow , what a rough time for your son.
He needs to decide if this is how he wants to live his life. Does he want to deal with this continued emotional abuse? Or does he know he can go on and be better off without this?
My ex used to do the same thing to me. Keep me on edge. He felt in control this way. Keeping me upset and uptight and willing to do anything to fix the relationship. I grew tired of it. I hated spending nights wondering, worrying and crying.
I finally had had enough. And moved on.
My life, feelings, love, was worth a lot more then what he truly wanted. He wanted someone who was at his beck and call. Every moment everyday.
But, it is up to your son. He will have to grow up handle the situation as it needs to be handled. He needs to step up to her. And stop playing the emotional roller coaster she is keeping him on.
Just reinforce the fact that he will 1. Have custody of the son, or 2. Have full visitation.
1. He needs to keep notes of this emotional abuse.
2. Document EVERYTHING.
3. Be ready for a hard road.
4. Get a lawyer.
Emotional abuse is hard to prove so the more he keeps track of what is going on the better things will be in the end with his child.
Again it is up to him. He will have to decide when he has had enough. And not until then can you truly help him. This is not healthy for him or his child.