I guess I'm a bit different from a lot of people, but . . .
I, personally, wouldn't get that upset if someone cheated once, especially if they were honest and apologetic about it. I'm not one to end something over a single episode of cheating. Everyone makes serious mistakes from time to time, including mistakes that hurt people they care about. It sounds like he did the honorable thing to do: be honest about what you did, admit that it was wrong, apologize and take responsibility. If I were in that situation, I would just forgive and move forward.
I'd say my success rate at "going backwards" is about 50%. If I still like the person, I always make an effort to remain friends. Sometimes it's necessary to take a break from one another until any emotions have cooled off. But often, having been intimate with someone seems to strengthen the friendship. Some of my closest friends are exes and former sexual partners.
So I guess anything's possible. It depends on what you're comfortable with and what you, and other people, want.