The group dynamic has changed. It's not your fault, but you need to accept it.
Dear Prudence,
A few years ago, I enjoyed being in a large group of friends who shared a lot of the same interests and would socialize frequently. In addition to regularly socializing at casual events, we traveled together several times per year. Three years ago, it was revealed that two of our friends, who were married to other people, had been having a long-term affair. One of the couples has since divorced (Amber and Ben), and the other couple stayed together (Chris and Delia).
Amber, Ben, and Delia cannot be in the same room as each other, so all of our traditions have been impacted. We now have to decide who to include and who to exclude from every trip and every social event. I am particularly conscious of Amber’s feelings because she is not at fault. I am currently planning a trip for a milestone birthday and I have invited Delia. I don’t agree with what she did and the fact that she has shown little remorse, but we have a lot in common and she is my oldest friend.
How should I deal with this situation (and other future similar situations) since I cannot invite my other two friends? I was discussing this trip with Amber and a group of friends, and I had to privately tell Amber afterward that Delia was attending the trip. It got really awkward and I felt bad. When I think too much about the situation, I feel angry at Delia for fracturing our group of friends (on top of splitting up a marriage and doing damage to her own family unit), and I feel like I made a mistake inviting Delia on the trip. I want Amber to know that I value our friendship even though I am still friends with Delia.
—Fractured Friendships
Re: The group dynamic has changed. It's not your fault, but you need to accept it.
Delia and Ben need to accept that it's their actions that created this situation. You can still be friends with Delia but I would stop feeling like you owe Amber explanations of all the things as well.
Friendships evolve and change. And if I was Amber and opted to salvage my marriage that would be the priority over activities with the friend group. That may also mean that you need to accept that your friendship with Amber and Ben may drift if you prioritize a friendship with Delia.
Just see your friends separately and don't discuss them with one another.
I would be inclined to exclude both Ben and Delia from everything going forward.
As someone with no true life-long friends (my oldest friend I met my Jr year of HS and is my SIL, but I have no childhood friends...because of moving) and someone who's made really close friends as an adult, I place a lot less weight on history. I'm also game for a lot of things, so finding shared interests with people isn't that difficult for me either.
I think LW screwed the pooch on this trip, but I think they should take the little germ of those feelings about Delia being an asshole and probably not a good friend, and let that grow for a little bit. I'm not saying LW needs to dump Delia forever, but putting some distance between them would probably be a good thing.
If LW wants to repair things with Amber, they need to apologize and prove through actions that they mean it. And also know that they may not get her forgiveness.
Oh and stop pining for something that was a total farce. They were playing in all of your faces, so all those good times and trips and whatever are completely marred by the affair.