Blonde,
Oh my gosh, you really are living a nightmare! And no, you should not feel guilty for anything. You didn't do anything wrong other than love the guy. You put your trust and love and your children into a relationship that you thought for for real, and a wonderful future. Little did you know.....You are right to be hurt and angry...I would be if I were in your shoes. I don't know why he wasn't honest with you upfront because he should have been. If it was real love it would have endured no matter what. However, now you are in the situation and you and your kids are going through a lot because of it. I can't really tell you what to do, but I'm sure if he gets well he will have a lot of explaining to do if he wants to keep you. And it sounds like you are a keeper because you are sticking with him through all of this. And if he can't be honest with you in the future, you may not want a future with him at all. As far as your kids are concerned, I'm afraid they would have to come first and foremost. They're probably scared right now and don't understand what's going on....Can his family help? It sounds like that's what you need right now..
Good Luck and I hope it all works out for you!