One thing that jumps out at me is that he has not come to terms with your EA and you have never come to terms with his affair, whether it was EA or PA. I do not doubt for an instant he was involved with someone. No man suddenly begins to go out until all hours of the night, several times a week, for six months and then just as suddenly stops unless he's seeing another woman.
To answer your question, you can go for radical honesty and total transparency in everything you do. Offer him the passwords to all of your email, instant messaging, etc., accounts on your home and work computer. Let him see your cell phone calls every day, ask him to review your cell phone billings, let him put a key logger on your home computer controlled by a password only he knows. Things like that.
Then, you can tell him who the other man is and agree to answer any questions he has about the EA. Radical honesty works. Try calling him at natural intervals throughout the day when you COULD be making those calls to the OM.
Then, of course, he needs to sit down and answer every one of your questions in the same manner you answered his.
To find out how to do all this, I suggest you order the book Surviving An Affair by Dr. Willard Harley. While you wait for it to arrive, read the "Most Popular Links" to get a grounding in MB principles. These are from Dr. Harley's book and will be a good preview of the full text.
Also, you two are prime candidates for couple's counseling by a good, experienced, pro-marriage counselor. If you can afford it, make an appointment with Steve Harley for telephone counseling. If you prefer a local counselor take the time to find a good one. The DO come in varying grades of competence, expertise, and orientation on the subject of marriage.
Let us know more about your situation, okay? If you have children, how many, sex, ages...children change the dynamic quite a bit. Your ages can matter also. In fact, you are anonymous out here. Don't be shy about putting all the details about the affairs into your post. Use this as a journal as you work on your problems. My thoughts are with you tonight. You'll find a lot of people out here have gone through what you are now and will be ready to help you. Welcome to MB.