She should think you are finished with her. Even if she accuses you of "quitting". She has to feel that you've dumped her b/c she has lied time after time. Don't believe anything she says.
It always amazes how fast a WW can jump from texting about why she just had to contact OM one more, maybe even throw in a "I'm sorry".......and immediately ask about the upcoming vacation trip all within the same range of texting.
Your boys are big enough they don't have to her along on the trip. Make it a guys only trip, and leave her home. I mean,...........seriously!
Resist the temptation of saying too much, Bern. Don't go into explaining things to her. She knows she is rotten! She may apologize and claim she wants to save the MR......but she was seeing OM as recently as when?
If she goes to you, and depending on how much she pleads for another chance.........this might be the opportunity to get her to agree to no contact of any type with OM.....ever. The WW will usually agree to that much, even when they don't intend to keep their promise. If she agrees, then tell her the only way you can consider staying with her, is for her agree and cooperate in being fully transparent.
As for you confronting her at this point, or going to MC just to see if she'll come clean........why bother? She's not going to tell you any more than absolutely necessary. She is a liar, and a cheater. Stop expecting her to act otherwise. Don't make any moves until you talk it over here.
I'm in a big hurry right now, and have to leave for a little while. I'll check back in an hour or so. Keep us updated.
((hugs))
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!