Not trying to be argumentative, but I would never recommend trying to enlist the help of the OM/potential OM in these situations. You're asking someone who -- if they ARE involved with our spouse in any sort of inappropriate way -- is a LIAR, and you're trying to glean something useful from them?
Confronting OM/OW directly is almost always a mistake. It:
- only elevates their importance
- adds to the "drama" that illicit couples love to thrive on
- is often perceived as weakness by them
- fodder gained from it is not to be believed, at best, and can actually MISLEAD you at worst
- conversely, YOU may reveal things that they will use against you
