DW I understand where you're coming from, I'm just imagining this poor woman waisting her life with this scumbag and I feel sick, I'd want to know. He absolutely wasn't having a moral dilemma at all, it's hard to realize when you're the woman involved with a man like that. Happy OP felt comfortable asking for advice.I'd be against telling her as it's more about getting back at him rather than concern for her welfare- not to be harsh and not having a go but it's a bit late in the day after 12 years to pretend to be doing it for her benefit. IMO the OP should leave them alone and focus on herself.
This is so true and I've done it myself many times, I've projected my feelings onto the guy. The OP believed he was going through some mental anguish because she was whereas in reality he was doing nothing of the sort.