I have a heavy heart. To make a long story short, a friend of almost 20 years has informed me she has started a physical affair with a married man she met on the internet. I actually introduced her to her husband years ago. Some years later he had forbidden her to contact me as he suspected I wanted to have a relationship with her prior to her marriage (he was right), but she has still called me occasionally over the years. The irony is that once she was married there was no chance I would ever do anything with her. I am sick about it (they have 3 children ages 5 to 14). I view her behavior as self-destructive. She claims marriage is lacking nurturing and good sex. She basically unburdened herself onto me and I feel like I'm carrying the load.
My question is should I tell her husband. She says he is totally content and unaware. She claims to be in love with this guy and he with her, but I think it's delusional. The guy is lawyer so he is probably good at manipulation. She thinks they're both trapped in their marriages (he has 4 kids), and he says he can't leave his wife.
I'm sick about this

Yes, you need to tell the husband. He deserves a chance to know what is going on and a chance to save his marriage before it is too late. Think of the children who's lives may be ruined. If you tell her H, you aren't the bad guy she'll make you out to be, she is the bad guy. She needs to face the consequences of her choices otherwise she may just destroy a family. You have a moral obligation to step in and do something? WWJD?

If you have any more questions post this on the GQII forum.

If the WW ever truly communicated her concerns to the BS he probably would have fixed the problem, but she has likely kept it all bottled up inside. Give them a chance. She is not "in love" with this OM. The OM is a lying, cheating, scumbag who will likely never leave his wife, he just wants some sex because he isn't getting enough at home.

Forgive me on the acronyms, I don't know them yet.
The H has always thought that I would be the one to do this. I love her too much to interfere with the family. She has kept this bottled up, she has a dark side that she has repressed since marriage. I'm am worried her H may get violent.

well all I can say is you know telling him is the right thing to do otherwise you would not be here.

Your fears about viol;ence are most probably unfounded. You are just trying to rationalise away your correct instinct to do the right thing. That type of BS has a short shelf life.

Tell him and get it over with.

How disrespectful of this woman to not only have an affair but to think so little of you to assume you would keep her secret.