How would you counsel your FDW if she tells you that her husband is seeing another woman?

It's harsh. My ex-wife cheated on me. So it's a lot of emotions. She needs to feel trust and safety right now. So do that first. Whatever she is feeling now is mostly reactionary. Let it sink in for her before you actually sit down and talk to her. By that I mean, you should be talking to her first, listening to what she has to say. Let her get it off her shoulders and after all that then you come in with what you think she should do. Me personally as a guy, would cut it off and move on. If there are kids involved, raise it up to my parents to take my children in. I would ask if your FDW wants to leave right now to go home and settle things. If she wants to you should let her leave and settle it her way.