Wow,
I think you need to be more careful how you are talking to your son, and not dig, dig, dig. Just let him talk to you naturally. Kids are smart and they can sense tension and emotions, even if they can't define them. Going through custody battles and all that doesn't make sense to him and there is not really a way to explain it to someone his age. Even if you think your ex was emotionally abusive, don't transfer that victim mentality to your son. Your son needs to see you strong and positive and happy, not asking something and then freaking out a bit over what he says and explaining how daddy is wrong. That will not help him.
I studied child development and divorce in a college child development class. I have also worked for years with special needs families. Numerous studies have shown that after a divorce, children feel very insecure and like they don't belong with either parent. So when he is with you, you need to help him feel as secure and calm as possible, do routines every day, and just move ahead with your life.
Also, society has taught women today that men are emotionally abusive and manipulative, and that women are victims. This is from feminism gone wrong. Usually (not always), but usually counselors will encourage divorce in these situations, and focus on the women trying to stand up for themselves and have their own rights. Be very careful with these philosophies. Women are very manipulative and emotionally abusive to men, too, but the counselors will not even ask about that side of a wife, or talk about it. Studies have shown that women and men are equally bullies to others, they just have different styles and men's styles are more obvious.
So instead of focusing all your energy on how bad your ex was, and likely he wasn't as bad as people are telling you, focus on making your home feel safe, routine, no digging, no fishing for information, no bad-mouthing dad. And pray to know the truth about yourself and your ex. You were probably both at fault in the divorce.
I hope that you are not angry with my advice, because I have been through near divorce with my husband many times, have been to many counselors that told me he was emotionally abusive, and finally, God showed me through a book how men think, and how mean they get when women don't understand them and treat them badly. I never thought or had tried to be a bad wife, but my eyes were finally open to how I had nagged, emasculated him, put him down, emotionally abused him, tried to boss and control him, all without seeing it in myself.
Take care girl, this is major stuff!
Marci