Regardless of what seems right, she will resent you exposing her situation. As she sees it, you are the offense, not the guy. So you just don't say anything.
Given that I don't know her. And I would still have to work the Mother of the cheater. No, I would not get personally involved as she is not going to believe it most likely anyway.
My friend since teen years was marrying his third wife. Not a big ceremony. The bride actually reported to her job later that evening. My friend celebrated his 'honeymoon' in bed with some 'chick' he found in a bar. Isn't love sacred?
There are classless people everywhere. Your friend's husband's behavior has no effect on my love being "sacred" or not. Trash. Society has always had to deal with it one way or another.
If I was close with the bride, she would get an earful. But getting involved can backfire on you. If I cared for her, I'd tell her even if I knew it could put a wedge between us because she would have a right to know. Some might say it's not my business, but I disagree - he made it my business.
Not Sure 