I am certainly not qualified to give advice to a counsellor, but I can tell you what I THINK I see.
Based on what you wrote, I have to wonder if there aren't some other problems going on between you and your hubby. Granted, this might have been a really horrible ordeal, but surely you two have been through tough times before.
Did he react differently than you expected? Was his behavior completely out of the norm for him? If it was, why did he react this way? Did he feel pressured by his family? Was he doing whatever he could to help his sis?
You say that you have some tough decisions and a lot of thinking to do. You have banned him from your home and his children. Did this situation really warrant these measures?
Please don't take this the wrong way. I do NOT mean to seem like I'm attacking, because I'm not. I have a really bad habit of playing the devil's advocate...drives my hubby crazy
I just wanted to give you some things to mull over while you are making your decisions. Is this whole situation worth throwing away your marriage for?
Obviously I can't know the whole story, just what you have written. And from that, I am concerned for you and your immediate family. Divorce is very difficult, and I don't believe it is always the answer. Of course, staying together isn't always a good thing either. I would just like you to examine your reasons from every angle to make the best decision for you and yours.
Please feel free to email me if you want some more hard questions. Some folks around here would say I'm full of it...er...them