I am going to have to go against the grain and say that I feel exposing the affair is never the right thing to do. Affairs always come out and the exposure is always far more spectacular when it comes out in an organic fashion rather that one spouse telling the OP's spouse.
I also feel when you invest so much energy into wondering if you should expose or not expose you are really taking away precious "Norm Time" and not GAL and working on you and what you *can* control. And you can only control you. And, generally speaking the OW/OM should be a non-entity in your world and no focus or time should be channeled towards the cheater(s).
Its too bad the OM's W will be hurt but such is life. OM and OM's W is not for you to worry about.
I think exposing an affair is a recipe for an explosion and it's simply too unpredictable. You have no clue how OM's would react and heaven forbid she did something outlandish (hurt her husband or your W for example, holidays and affairs don't mix well) you would have to live with your participation in the exposure.
Is your W still at home? If so you need to pack her up and send her on her way. IMO that would make a bigger impact as OM won't be able to house her if he has a W at home. If your W is gone already then go dark and set your boundaries. I feel the best way to handle infidelity is via the legal system or a very trained counselor if your W agrees to cut off ALL contact w/OM at once. If you want her to take pause start the legal process and show her the consequences via that route.
