Hope, I know how you feel. My W told me earlier this month that she thought she was pregnant with OM's child. It has now turned out that she isn't pregnant, but I know the emotions you are going through. It's awful.
I think the best thing for you right now is to completely quit talking to him. Go absolutely 100% dark. It will have a great benefit to your emotional state. You need time and space to recover from this news, whether their is any chance for your marriage or not. I would advise you not to see him, stop taking his calls, stop focusing on him, and truly GAL now.
The LORD is near to all who call on him, to all who call on him in truth." (Psalm 145:18)