hedgehog, I read your message with such admiration. Coming from an abusive family, I'm still angry with my mother for not protecting us children, and agree with other people who've written that divorce is far from being the worst thing that can hppen to children.
The issue of being programmed for abuse, its one of the hardest things anyone can do to break patterns from the past. You are incredibly brave and I admire you so much.
The situation you have been minpulated into by your ex-husband sounds particularly painful, and it must be extremely hard to know you are doing what you are doing for the children and yet have them see you as the bad one. It sounds like a case of "change back" behaviour, where others can't accept the changed you and want to return to a previous situation, however damaging it was.
Perhaps the children are doing what you suggest you did as a victim of abuse, clinging to or seeking out a similar abusive situation.
The only suggestion I could make as to what to say to them about him, is that although they have the right to believe that he has changed, you don't believe it and you have the right to believe that, and also that you don't want to take the risk of putting them at risk or in a situation where they could witness abuse again.
I can't express enough my admiration for you, and my belief that however hard it is, what you are doing is essential for the emotional survival of your kids and of course, yourself, and you are all worth it.
Perhaps you could print out some of the responses you've had here for the children to see when they're older.
Two more things: one is that you are finding the good in what seems a bad situation, by leaving, and the other thing is that ideally a good counsellor would help, but try reading Carl Roger's book On Becoming a Person. It is serious, affirming and it is heavy going, no miracle cures.
You have broken the pattern already. I'll be thinking about you.