This response is the scorched earth approach, which will likely result in a whole lot of recriminations from all sides. Sometimes, people already know their spouse is stepping out but choose not to act on it for their own reasons. The wife may not be grateful to have it aired out in public. And this may have been just a one-off lapse in judgement. The guy has already apologized. The letter writer could just let it go. Or she could raise the issue of cheating in general terms with the guy's wife, eg: "So Brad and Angelina are divorcing. Do you think he cheated with her before he and Jennifer broke up?" Then, casually ask if she would want to know if her husband ever made a move on a friend or co-worker. If the woman has any brains - or suspicions about her husband - she'll get the message. But she can still save face and the friendship may just survive.