We all slip from time to time. You have to try to calm yourself down and start to detach. Give him the space he wants. Begging him, trying to reason with him will not help right now and will only push him further and further away from your M.
If you can get your hands on the book Divorce Remedy by Michelle Weiner-Davis I suggest you read it. It will help you to understand what H may be going through and will give you some ideas about how to proceed. Try to find one or two things you can do for yourself. Also keep yourself busy with your D. This will help you to detach and get your mind off R (at least for a while).
I'm also going through a rough week. I know that H is more actively pursuing a R with OW. I have a lot of anger about what he's done but I've tried not to let it show in the last couple of weeks.
Me47 H46 S13 M16 Piecing since May/09
"Life is 10% what happens to us and 90% how we react to it." Lou Holtz