I would emphasize to W that you are a H...not a trained therapist. It is incredibly unfair for W to unburden you with this HUGE problem that she refuses to seek professional help to sort out her thoughts and feelings.
Also tell her that it is very, very difficult for her to talk to you about her feelings for another man, being afraid to date, etc with her OWN husband sitting right in front of her. I think it's time for you to draw a line in the sand on not talking about the OM with you. Again, you are not her therapist and you are not trained to help her sort those emotions.
