Putting a marriage back together after an affair is one of the most difficult things a couple can do. First, is everything out on the table? We used to think that it wasn't helpful to dig up the details. Now, we know that that it's better to have the details out so people aren't wondering. As one woman said, every time she passed a hotel, she wondered if that was the one her husband and his girlfriend had gone to. When she knew which, "then I only had one to deal with."
Truthfully, you are probably going to need more than I can give you on a forum. Marriage issues, especially where forgiveness is needed, is something that is often well managed by pastoral/christian counselors. Many churches have such a service available.
I'm going to send you a link to a good resource to help you and he have this conversation. However, ultimately you and he do have to have it. (I'm not affiliated with this agency and won't benefit if you buy the book.)
Getting Past the Affair: A Program to Help You Cope, Heal, and Move On-Together or Apart - By: Douglas K. Snyder, Donald H. Baucom, Kristina C. Gordon - Christianbook.com
This wound will only get worse if neglected, and you and he will need some help talking through it. Healing is a process, not an event.
My thoughts will be with you. I know this is a terrible experience, and we'll be here if you need us.