Wow, coconut, parallels keep popping up between yours and my sitches. I, too have a good friend (possibly my best friend) as you know from reading my threads, whose W (although in his case his wife is currently separated-- actually a WW) was supportive of my own W's A. (Our wives are also best friends and that's how my friend met her). Come to understand that I don't think she was a "rah rah go get that OM!" cheerleader, BUT... under the guise of wanting her friend (my W) to "just be happy", she participated in the A cover up and hung out at some social situations sith my W and OM.
For me, this gets particularly tricky because my own best friend is still completely convinced he can get back together with his own wife by "Being her best friend" and "always being loving and being there for her" and basically appeasing her and looking the other way whenever she has an Affair. This would include the A she is currently having (though, yes, they ARE separated) with a mutual friend whom he HAD considered HIS best friend back before the affair came to light last fall. At any rate, he has now become a "man of faith" (absolutely genuine and sincere, I am convinced... and I am one myself) after having been an avowed atheist, and places his loyalties/priorites in this order: God, WW, Children, friends (of whom I am one). He will hear NO ill words spoken of her and says he "wouldn't care anyway because he instantly forgive s her for anything she does wrong" which "gives him peace."
So, yeah, I really can't say anything about his W enabling my own W's affair without damaging that friendship (which has already happened to a small degree) and, besides which, he thinks I am totally ill-advised to be doing anything manipulative or investigative WRT my own W and that if I am not doing what he is doing I will "never be happy." IOw, he wouldn't at all blame his own W for her role in my W's A because he would say my W, like his, has to "go on her own journey" pretty much even if that means sleeping around with half the state... or at least over the course of three other A's as his own W has.
So, yeah, pretty tough dynamic, and I understand. As Sandi says, you probably just have to let it go. If someone says something hurtful about you, I would probably try to correct the record, so to speak, but beyond that you can't control what others are doing.
Sorry if that seemed like a bit of threadjack, but I get where you are coming from
H53/W51, R-ing 4/'18
"Do not arouse or awaken love until it so desires"-Sg.of Sg 2:7
"So oftentimes it happens,that we live our lives in chains, & we never even know we have the key"-Eagles III 1:3