I'm sorry that you are going through this. I would hope that she has learned not to cheat on her husband... ? any sign of that? probably not. grrr....
Maybe next time he could find a woman to really
sink his life into, for your sake and everyone else's. It really is a far better ride that way and can blossom into loveliness.
I hope his heart heals quickly and he realizes that cheating on someones husband is not
successful poly (IMHO).... he is lucky to have you by his side... know doubt you will have a wet shoulder.