I have counseled an old and dear friend just this week on this very subject. I empathized with her (her husband told her he doesn't love her anymore ), but told her she and the other guy should BOTH be unencumbered (S or D) before they go down this road, and that she would only end up heartbroken and despised.
I also told her, based on just some cursory questions about her OM and his family, that this guy is NOT going to leave his wife and kids for her! He'll TELL her she will, just to get in her pants, but he's never going to do it and she's only going to be even more disillusioned when this all comes crashing down.
), but told her she and the other guy should BOTH be unencumbered (S or D) before they go down this road, and that she would only end up heartbroken and despised.