I'm sure I'll hear the "I was thinking about getting back together with you..." line. So manipulative.
DOING THE RIGHT THING. Not always clear. Is doing the right thing confronting her or pulling way the hell back and not speaking with her and let her go. You've mentioned both and that I should confront first. Torn. Some of the things said on the link including letting her family members know of the OM will humiliate her and end any chance pretty quickly it would seem.
It often seems that way. Rarely happens, however. After they get over their initial LIVID-NESS ("lividity"??), they usually calm down, and sometimes even a nicer, more respectful wayward emerges, thru some combination of genuine respect toward your strong stand and some "play nicey-nice" legal stance perhaps.
Look, we could debate "2a" vs. "2b" all day long. All I'm saying is, WHATEVER you do, you do for your kids, and for you, and because it's The Right Thing to Do, NOT because of how angry it will make her, and how uncomfortable that anger will make YOU feel in the short run.
Once person's "humiliation" is another one's "consequences."