You need to read the chapter on infedelity in the Divorce Remody book. It has helped me understand how to cope with this. Even though I am still caught in the latter part of an A, my wife is trying to break it off. It still gives me hope that I can overcome this. I'm sure I will feel and already feel the same things you are, but I know GOD will give me strength.
I don't have the book, but I'll try to piece some things from it.
1. ask questions about the A, only if you can handle the truth. If you can't then don't put yourself through that. But sometimes the truth is better than the assumptions you are having.
2. Forgive him, forgiveness is not a sign of weakness, it's a sign of strength. You won't forget what happened but it will help start the healing process.
3. Find out why the A took place. that will help with it not happening again.
4. You will have doubts and bad thoughts all the time, when your ready you will have to put a stop to them. When a bad thought starts you have to conciously tell yourself to "STOP" and start thinking about something else. As time goes on you will not have to force yourself so much and it will get easier.
5. Ask for reassurance, he should be able to give you some when you need it.
6. When he is late or somewhere you don't know, ask, but in a positive way. If you are accusing him of where he is, it will make a negative conflict occur and will push him away.
7. Start on regaining your trust back, by all of the steps above will allow you to build that back up.
My W's uncle still deals with this after a lot of years. He said it's hard and bad thoughts still roam through his mind. But he needs to ask in a positive way and trust that the truth is what he is getting. You will never be able to forget what happened, but you can forgive him and if you want to be with him, you need to be strong. Change your marriage to a much stronger one, make the changes which caused the A to happen in the first place. Make sure that you never get into a situation that will put your marriage in jeoperdy again. Ask for GOD's strength everyday, HE has the power to heal.
M-31 W-25 S-1 1/2 bomb dropped 9-01-06,and repeating over and over "I, not events, have the power to make me happy or unhappy today. I can choose which it shall be." Groucho Marx.