Bit of a debate on this going on over on AIBU.
This question isn't really about me, but 15 years ago my first husband had a short affair, and when he ended and said he was going to tell me the truth, the OW was fuming and beat him to the punch / contacted me as an act of revenge. I remain sure, finding out this way made the whole thing far more traumatic.
I do think though, in an infidelity situation, if both cheaters are married and one finds out about the affair, that it's a very good idea to tell the other spouse. I think the two victimised spouses can be good allies in exchanging information and ensuring the affair is over and no worse damage is done, as well as enabling both people to look after their family / kids and home.
So the question is:
If you have experienced your spouse having an affair - how would you feel about:
a) The OW phoning or writing to tell you
b) The other betrayed spouse phoning or writing to tell you
For me, the former would almost always be an act of cruelty and / or revenge by someone trying to deliberately hurt you or get rid or you or use you as an object of revenge. If they were worried about your feelings and wellbeing, they wouldn't be shagging your husband. So I feel this act is almost always motivated by a misguided belief that by blowing up the marriage, you will get rid of the wife and pave the way for yourself to be the new wife, or alternatively to wreak revenge over being rejected. For the wife, IMHO, this is one of the worst ways to find out and is very cruel indeed.
If they were not aware your spouse was married - and are genuinely doing it because they "felt you should know" - then they have the option to say to your spouse "you tell her or I will". However, I am still not convinced that isn't revenge based!
By contrast, I would have been happy to have been told by the OW's spouse, had she had one. I would have considered this person a "safe" person who was my fellow victim and I would have felt pleased to have known and be given the opportunity to ask questions to ensure answers matched up and so on, as well as to know it was unlikely I would have continued to have been lied to and harmed.
How would you feel?
It's probably better if people who have been actually cheated on in a marriage could answer, as I honestly believe if you haven't been you can't possible know the trauma and pain of it and how dangerous the OW feels at that time to you.
Certainly before this happened to me I could roll out many lines of things I would do if it ever happened to me, but nothing but experiencing it prepared me for the reality.