Umm..I dont know if any other ADers have experienced what M and R are experiencing but I have sort of experienced a similiar thing with my ex hubby and then again with some of my good friends.
When my ex hubby was cheating on me with one of my brother's Gallaudet friend's girlfriend at the time I was a Gallaudet student, almost everyone in my circle of friends at Gallaudet knew about the affair except for me. They all tried to tell me what was going on but I refused to accept what they were saying because I was in denial and wasnt ready to face it. Instead, I got angry with my friends for trying to ruin my marriage and pushed them away. When I finally knew the truth, I felt ashamed but I wished they didnt get involved because it was too overwhelming to have so many people involved with my marriage problems. It drove me crazy. I needed to be ready to face it and be ready to address it. I couldnt handle my friends telling me about it and pushing me to address it. I did appreciate their help but emotionally and mentally, I wasnt ready.
Then, one of my friends cheated on her es-boyfriend (who was a friend of ours) with another friend of ours and told many of us to keep our mouths shut. I was so conflicted just like you were but didnt say anything. However, my brother did tell her ex-boyfriend about the affair but he beat up my brother cuz he thought my brother was trying to steal his ex-girlfriend. Then it became a HUGE soap opera drama within us and a lot of friendships were ruined. Yes, they broke up and the guy that she slept with is totally out of the picture so many of us wondered if it was worth telling her ex-boyfriend about his GF's affair with our friend.
Since then, I have always stayed out of other people's relationships. Right now, my friend who is also my co-worker just found out that her husband had been having an affair with another coworker /friend and all I can do is be there for my friend for emotional support but I wont go around judging my friend's hubby and his lover because I dont have both sides to the story.
That's why I always stayed out of these kinds of things. The less people are involved the less complicated the affair/situation becomes.
Affairs are just not worth it and people who have them should break up their current marriages or relationships before having a romantic relationship with another person.