I need some advice, please!
My hubby is best man for his best friend's wedding. His best friend's brother is a groomsman in the wedding and the brother's wife is a bridesmaid.
In discussing plans for the bachelor party happening in a few weeks, the brother told my hubby that he is planning to skip out for a few hours to see an ex-girlfriend (and cheat on his wife), but he doesn't want anyone else to know. My hubby told the brother it is a bad idea and he is risk ruining the bachelor's party (there's only 1 best man and 2 other groomsmen, so his absence will easily be noticed by groom) but the brother doesn't think it should be a problem.
My hubby is afraid to tell his best friend about the brother's plan because he is afraid that telling the groom could potentially ruin all of the wedding plans (since his wife is a bridesmaid) However, I'm afraid that if the groom later found out about what the brother did (using his bachelor party as opportunity to cheat on his wife) and also found out that my hubby knew about it ahead of time, my hubby could risk losing his best friend.
My hubby asked my opinion on what he should do... so now I know about this plan and feel like keeping it from the groom, who is a good friend of mine, and his fiancee, who is also a very good friend of mine, is a form of betrayal.
My options to my hubby were the following:
A) Have my hubby talk to brother and tell him he should talk to groom about this first, and also tell the brother that putting my hubby in middle is jeopardizing his friendship with groom, if groom ever found out, and see if brother will either cancel plan because he doesn't want groom to know or talk about it with groom and then it's out of my hubby's hands

Hubby to tell groom and keep his friendship and loyalty to groom and say "forget you" to the brother, since they are only aquaintances through groom
C) Somehow convince groom and other groomsman to move party to different location, since no reservations have been made yet anyway, and hopefully prevent the brother from having opportunity to cheat
Any other advice from anyone out there?? I feel like I'm caught up in this too, since I am good friends with bride and groom, and also the MOH......
Thanks for help!