ColdFront, I have so much respect for your courage and your integrity. And I can feel your pain over losing your friends and your entire social ecosystem.
Even as a BS, I don’t experience the infidelity as my only loss. My husband’s AP was married as well. On D-Day, the other BS didn’t just cut contact with my WH — he cut contact with me too. My guess is that he was afraid of hearing things from me that he simply didn’t want to know. Before D-Day, the four of us had spent time together several times, so I had known both the AP for many years and her husband as well. That loss still hurts. Partly because he is the only person in this world who went through exactly the same thing I did, and partly because he took away my chance to have my information validated (that's another story though).
The AP had two confidants who both knew what was going on. All of us had been part of the same community for many years and had known each other well for a long time. While my WH and his AP have since left that community, the two people who knew and I are still part of it. That community is incredibly important to me because, besides those two, some of my closest friends are active there too. It gave me a lot of stability during the hardest, earliest days after D-Day. And yet, every time I run into those two there, it’s still awful. At some point I confronted them, but the only thing they said was: "We didn’t want to get involved. It’s really none of our business." On top of that, the AP obviously told them that my WH had been pursuing her. I guess the idea was to make it sound like she had barely been able to defend herself... 
Other losses involve friends who simply couldn’t handle the fact that I didn’t immediately decide to leave my marriage. They either withdrew completely or now maintain only a very surface-level, functional relationship with me. You might ask: Were they really friends? I certainly believed they were. They were people who played an important role in my life. I grieve those losses too. My entire social network has been torn apart. And nobody asked me if that was okay.
Again: I am incredibly impressed by the decision you made. You can walk through the world with your head held high. If you had stayed silent, your friendship would have been severely damaged as well — if not eventually ended altogether — because I doubt you could have lived with carrying that secret either.
