I am going to go against the grain (and Cooley's advice). Cooley advises to ask the following:
Do you want to stay married? Are you ready to divorce? I think it is time to sit him down and ask him if he enjoys being married to you. Also ask if he loves you. If he says yes to both then ask him why he is doing something he knows will hurt you. Then let him talk.
I like the questions for YOU - but the questions for him??? Forget those. I mean REALLY forget them. If you ask his answers could be out and out lies or total honestly or anywhere in between. You may as well flip a coin with one side saying "yes he 'loves' you" and the other saying no he doesn't and go with what the coin says. It will be no less accurate and decidedly more clear and understandable.
The more important question would be: Even if the answer is yes he "loves" you and yes he wants to stay married to you, is this the version of love and marriage YOU want?? Again, forget about what he wants. Seriously, this whole marriage thing is a two-person deal. If you are not satisfied with it then I say you need to tell him what you need to stay in it and to hell with what he wants.
I would say, look, I know you are talking with old so and so...again. I told you before - you are well aware - that her being in your life is not okay with me. I was 100% clear that our marriage was not to include her, yet here you are, back at it again. I don't care if you had sex, fantasize about sex, talk about rainbows and pots of gold or talk about saving endangered species in Africa - none of that was acceptable for us to continue, yet you decided that engaging with her is worth risking our marriage. Fine. If this is your version of love, if this is the version of our marriage that you have decided is acceptable to you, you can keep it. It is not my version of love and continuing communicating with her tells me that my version of marriage isn't what you want either or you wouldn't be doing this. So think about what you want to do while I tell you what I MUST have...
and then go ahead and tell him what that is. Once you have said what you want, and presuming he says he will give that to you - respond with a simple "I don't want words. You're going to have to prove you mean it." If you don't it will be clear. If you think I am going to "get over this" in a few days and "wholly trust you again" anytime soon, and that you aren't willing to prove it knowing that, then don't bother.
Seriously - don't bother. I SOOOO wish I had said that from the get go. Would the result on my WH's end been different had I done that? Who knows, but MY life would have been a lot less long-term miserable. Ripping off the bandaid is what I should have done instead of peeking in, seeing a festering wound from time to time, negotiating with how to treat "my problem" with my WH who clearly did not have my best interest at heart AT ALL (as he was balls deep in looooove and luuuuusting after one of his best friend's wives), covering it back up, and taking an aspirin and hoping it would go away.
And BTW I WISH I was badass enough to have said something like that on d-day 1. On d-day 2 I was much closer. And, oh yeah, on d-day 3 it was all that and more. (*dday for me means ongoing A or new A that was not happening as of the last d-day - so I had 1.5 years of false R with an underground A. I GET how it feels to have discussed something affair related and have it disregarded - totally.)
EDIT: Sorry, I'm a bit feisty today (not that I don't mean what I said - just that normally I am a bit less heavy handed). I just think back to my early "negotiations" with my WH and it reminds me of the whole "we don't negotiate with terrorists" policy various governments have. That's what I should have said to my WH from the get go: This isn't a negotiation. I don't negotiate with terrorists.
[This message edited by ThisIsSoLonely at 8:53 PM, Tuesday, May 23rd]