I don't have any advice but I'm sorry your dealing with an om, it's so hard isn't it!
My h was in an ea last winter with a neighbor, she had filed for d from her h, and calling my h all the time, spending her nights with my h playing cards, watching football, and they both were divulging how horrible their spouses were to each other. I couldn't take it anymore and had a talk with her one day explaining how I felt in which she said she was sorry and never thought about me because she was so distraught . I also ask my h what's up? Told him he was being disrespectful to me , giving his time to ow, talking about our personal problems to her, etc... His reply was anger, and of course that they were just friends. They started hiding there interactions more after that, but he wouldn't do one thing pertaining to her that I ask him, wouldn't even admit it looked bad from where I was standing. He said if I don't trust him we had nothing, and that I'm crazy and controlling for trying to make him get rid of his friends. So I know your in a bad place. Nothing I said changed anything with the ea they were having, in fact it made it worse.
M 2005 ~together 1997 Bd 2006 & 04/02/2014 1 dd 12 H~ 44 Me 48