You are absolutely making the best decision that you can in your current situation. Unfortunately, your son most certainly can develop nasty traits of your husband's...even if he is angry or hurt by what he has seen. I would therefore be sure to support him in the most helpful ways.

I do agree with Rose76 who questioned whether you should be devoted to obtaining an amicable divorce. I think that isn't always the "right thing to do", especially when you're removing yourself from an abusive marriage. Imo, the right thing for you to do is to focus upon YOU and YOUR SON. That's what is most important. If you're going to split custody of your son 50/50, then you're going to want to leave on the most positive note that you can, to help your son cope with the major changes in his life. But, if you're shooting for primary custody, forget the relationship with your abusive hub. You and your son need to be treated decently, with care and respect!

Very best wishes to your son and yourself ~ take care!