Do I tell the bride he’s cheating?

Folks, I looked today, and we're almost to our 10,000th comment. I think the person who is the 10,000th commenter should win a prize or something. That's pretty big. I'll let you know when it happens. This one's about disclosure.
I recently met a really nice, funny, attractive-in-all-the-right-ways guy. My friends and his friends met out one evening and hung out for a while. We were then invited to one of the guy’s homes where the fun flirting and attraction continued. We stayed until the following morning. No sex -- although he wanted to and asked many times if it could happen. The morning after, the four of us laughed, drank coffee and he asked for my number for the second time since meeting. While in his friend's kitchen I came upon a rehearsal dinner and wedding invitation – with just a first name on it. It was his name (which is a very common name). I joked that it was his. He said it was a friend’s. I took note of the web address on the invites. Later I visited the website and discovered it is, in fact, him getting married this mid-July. The website shows photos of the life he has lead for the last 3 years with his fiancée. I feel bad for the woman. She is marring a man who completely disrespected her and the relationship. There is an email to contact on the website which is hers. Should I give her a heads up as to her fiancée’s recent activities? Or should I let karma take its course? Also, what is up with guys? -- AnswerThis, Boston

AT, some of my readers are going to tell you that this is why you shouldn’t go home with strangers. But that’s not really the point of this letter, is it? You’re upset that you were duped -- but you’re more concerned about this person’s fiancée and whether you should e-mail her to let her know what she’s getting into. This question comes up a lot – whether a third party should inform someone in a couple about a cheat. The thing is, there is no right answer. All options feel very, very wrong. If you tell, it’s possible – and probable – that the fiancée won’t believe you. You’re a stranger, after all, and he’s probably a great liar. If you don’t tell, you’re withholding information that could save this woman from a partnership rooted in deception. My advice is to e-mail him. Find his contact information through your friends. Tell him you’re very sorry he lied, not because you can’t handle it, but because you assume he’s marrying someone who believes in him, someone who deserves much better. The note probably won’t do much – but it couldn’t hurt for him to have a little scare and a reminder that his actions have consequences. That’s the best you can do. As for what’s up with guys … Guys? Want to field that one? Do all men do this? I hope not. Everyone, share thoughts here. Letters to the right. Twitter here. -- Meredith