I am going to read up on your sitch but I just wanted to say I think an important thing for people to realize is that an A has to run its course. We so badly want to break it up or do things to stop it but a lot of the times if you act out it brings them Closer together. I made sure all my family and H's family knew about it ... But not directly from me (didn't want H knowing I cared enough).
When things go sour - you have to be the better choice, the person your H or W fell in love with from the beginning.