In the sixties and seventies, it was the common wisdom never to mention a spouses cheating. this made sense at the time, as the potential for harm in the revelation was far greater than any potential good.

In the modern era of HIV /AIDS though, it is absolutely a matter of public health to let anyone who believes their relationship is monogamous know that they are being cheated on.

People who enjoy the risk of cheating are also people likely to have unprotected sex.

Please, PLEASE don't let an unsuspecting spouse spend his/her lifetime struggling with an illness they weren't responsible for, simply because you fear the awkwardness of a revelation. Do it anonymously if you have to, but do it! ! !

I don't know if I agree with TruCelt's primary reason (health risk), but I agree with the conclusion. Tell the spouse. I would tell her out of loyalty to her (i.e. because she's such a good friend) on top of my feelings about the morality of her husband's actions. If she wasn't a friend, I wouldn't do it, although I would tell the cheater what I thought of his/her actions.

But what if, as seems likely, the wife strongly suspects that the affair is taking place? There may be a hundred reasons why she prefers that state of things, rather than bringing it out in the open. And her friend telling her will put her in a situation she may not want to be in: now that her friends know that she knows, she knows her next move will be scrutinized. In this case I agree with Prudie.

I used to be of the school that you should always tell the 'cheatee' if she (or he) is a close friend, but more and more I've found that people resent the person that told them and they feel embarrassed that you know their private business, especially if she forgives him. I've been on both sides of this problem, so I know how hurtful it is to discover that everyone knew and no one cared enough to tell you. The LW first needs to discuss with her husband how he would feel if she divulged this confidence. Next, she should plan for the worst case scenario - that 'Anita' never wants to speak to her again. If she still thinks that telling is the right thing ... then maybe she should. Yes, sometimes people stay in relationships despite the gut feeling their partner is cheating. But I think the lack of direct proof keeps him or her from leaving. I'll bet 'Anita' hopes that it's not true and the fact that he would (brazenly) invite his girlfriend to socialize with his wife might confirm in her mind nothing is going on. I hope that the wife doesn't eventually find out, maybe the LW could suggest that her friend hire a private detective.

I meant to write: I hope that the wife DOES eventually find out.

I understand what you mean about respecting your friend's wish to maintain a particular state, but by the time you know about the affair, that state has changed. I like to think that if we are such close friends, she can tell me that things work for her the way they are and that the best thing I can do as a friend is keep my mouth shut. It's a hard call, but I would tell my friend because (at the very least) I think she is missing some information - namely that the situation she thinks is contained is not. Not to mention the whole wedding vows, bad husband, you deserve better, etc. group of reasons.