Now repeat after me…
“Not my circus. Not my business.”
It’s really not your place to interfere. There could be much more complex issues going on in the background, of which you’re not aware. And by interfering you could potentially destroy a delicate system.
Granted, chances of this are slim, but it’s just not your place to interfere unless you are a superman of sorts. If your full name is indeed “Relationship magician," then run quickly for the nearest phone booth, suit up and do your shit.
Otherwise back away slowly, and keep out of other people’s business. You can’t be certain that the husband is unaware. He could have a history of sexual abuse from his childhood, and have an understanding with his wife regarding extramarital activity. Your interference is not necessary. Although your intentions might be good, you might wind up causing pain and turmoil in your efforts to rescue the Relationship and Marriage world.
Some people will blame *you* for bringing it to them. They are like the woman who would punch you for stopping their boyfriend beating them. It might be the right thing to do, but that doesn’t mean you can expect the person will appreciate it.
Some know/don’t know - they know, but prefer you not to disturb their pretense that everything is fine. Some woman I know, knew her husband was, and simply never wanted to know who he was cheating with. One woman has known since she was a teenager and has stayed with the man for almost 20 years. He’s a serial cheat. She knows/doesn’t know. Whenever someone tells her she shuts it out.
Cheaters will find conquests even if they have to pay for it. Your friend may not be the first, may not be the only, and may not be the last. It seems like this new found urge to tell has more to do with you. Afterall this affair has been going on for years without you doing anything. Something has changed for you and that something is for you to manage for yourself.
Instead of taking revenge on behalf of your friend, you can save yourself drama, move out and move on with your life. Unless you're addicted to drama, you might like just like to move on with life, have fun and enjoy all the good life has to offer.
You never know - if your own sex life is steaming hot - it might just might help refocus your attention to it. Hehe.
Some friends may question themselves and say, "Well - what if my friend finds out that I knew and did not tell them?' The real culprit is the one who didn't keep it in their pants and not you.
However, If you do wish to inform someone about their cheating spouse, I'd say go anonymous. Write a clear, precise letter by hand or safer still, look for their email address and send an email from a newly created 'no trace email' and sign off as a "well-wisher".
The chances are that the person whom you inform anonymously may take you more seriously and also, you won't become a victim of "shoot the messenger". Focus will be on the message rather than the messenger.
She may already know. Perhaps she has deliberately chosen to do nothing. What she does with the information is her business. You can only intervene in this situation once.
Make sure in any case that nothing can be traced to you to avoid unnecessary drama. Needless to say, I'm presuming you are doing this as a good deed to help a lady identify her husband for who he is and you don't have any ulterior motives.