Of course (selfishly) the last thing that I want is for OM to suddenly become single, fully available, and looking for someone to comfort him.
I can understand that thought, but I still don't think it relieves you of the moral obligation, as it's still a selfish (yet perfectly understandable) stance.
If you knew the foundation of the woman's house had a crack in it, and the building could possibly collapse . . . wouldn't you let her know?