With that said, I am a newbie here still on this board and also in my own divorce situation. Hardly qualified to give advice.
The older guys should address your Qs because they know you better IMO.
But I have to ask you something. How old are you and do you have any children with this man?
It sounds like you are still young and do not have any children. If true then from what you posted here he is IMO not worth fighting for. I would just cut your losses and initiate a divorce. I hate saying that because my own D was the most painful experience I have ever had but in your case I would say I would do it.
Sounds like he needs a reality check and you need to get on with life. Lots of guys out there that would kill for a good woman and would not do crap like this to you. Ask me how I know, hell I am one.
But realistically, You are in shock. I have been there. For now just do nothing. Let it sink in first. Like any patient in shock you have to stabalise them first and then treat the wound.
Sleep on it for now and check back in a day or so.
Me:48 W:55 M:22 T:23 Bomb:19Nov09 S:15Jan10 D:11Feb10 EA:Confirmed on 20Apr10 Fast track to her divorcing me