Sadlyseattle. Your children are no longer children, as you say they are adults. The Bible us tells that children are to honor their mother and father. Not just one.
It sounds that you are still making excuses for your former husband. You are allowing a situation that YOU gave up on at least 7 years ago to rule your life now.
You say that you don't want your children to know the type of man he really is, so what is that saying about the type of woman you are? You have sheltered this man (not the children), and you are still sheltering him. When will you allow him to grow up? And when will you get on with your life? Sometimes, we have to let our children go, and let them find out for themselves what is right and what is wrong.
The best thing you can try to do is to tell them the truth about him. BUT you may have waited too long, and it will just sound like sour grapes to them.
Go live your life, do your best to stay in touch with your children, and let them find out the truth if they ever do.