So many wonderful comments and email messages to help this guy through his rough patch with his friend. In my immediate response, I told him I would do a post and suggested he read the responses you, my Faithful Readers, would supply.
I hope he follows the really good advice you provided. One common theme was that his friend might be suffering from enormous guilt, feeling as if the activity was a betrayal of his wife.
In the message, it didn't appear as though the writer hoped for a continuation of sexual contact; just a return to the sincere friendship.
I have no doubt that it will, that their relationship will survive this episode. It will just take time, and perhaps some outings with a group of mutual friends.
Outings where there is nothing to fear.
This blog (I hope) provides a means of sharing information with one another, helping one another.
Thank you to everyone who responded.