I would not recommend contacting OM or making threats to reveal the A to his primary partner. This will not solve your problem which is your W's EMOTIONAL attachment to OM. In fact, you contacting ("messing with" in her view) OM, is likely to increase her feelings of loyalty to OM.
I know that the idea of physical contact between OM and W is painful for you... but try to remember this: Your W's EMOTIONAL connection with OM is the primary PROBLEM, not the physical side of the affair. She's a woman...once her emotions for OM resolve, there will BE no physical side to the affair! True, physical contact can indeed increase emotions and bonding, but so can the "missing" and frustration of staying away from physical contact and e-mailing eachother about the agony of it all, so I would try not to go crazy over what she does or doesn't do.
I think the whole "chapperone" idea was kind of bizarre anyway, not that you asked for an opinion on that ... but how can two people have a private conversation with a chapperone sitting there? Jeeze, there would be more privacy on e-mail!... OH, I forgot.. except with a snoopy H!
I would not take this "last meeting" biz so seriously! Often there are many "last meetings." I don't mean to sound pessimistic, but you will avoid a lot of stress if you don't get sucked into their drama.
I think you might sit down with W and GENTLY inform her that she does not need to SEE OM to "cut things off!" There is such a thing as a telephone. And e-mail. I would gently ask her why she feels she needs to "see" OM to break up. They want to see eachother because A.) they want to be able to have physical contact or B.) they plan to continue the relationship. If you could gently get her to fess up which one it is (or both) it may lead her to some self-insight about what she is really doing. Right now, she's kidding herself. People don't go to hotel rooms to break up!!!!!!!!!!!!!!!!!!!!!!!!! Next you are going to hear that they want to take a 2 week "break up vacation" to Aruba. Just for one last visit! I am ALL for you supporting your W about this and letting her do what she wants to do! But that doesn't mean you have to act like you "buy" all her transparent rationalizations. That's not going to help her "reality check." I think you can gently make known that you don't buy rationalizations, and then hopefully she will respect that she cannot pull the wool completely over your eyes, even if she can pull it over her own.
