Well, just so you know - ultimatums on ending things with OM, including quitting jobs, is often what is needed. Otherwise the temptation to slide back into an EA or PA is too great. Harsh as it sounds. Some couples have even moved to a different state. I don't know if such drastic measures are always needed or not - I've obviously not been successful in my own sitch. It doesn't take much searching on google or looking through books, though, to see what most marriage counselors recommend. For instance, google "mayo clinic marital affair" and you'll see a standard example.
I think your H giving up after an ultimatum isn't met is unfortunate. As many people say on these boards, the betrayed spouse should shine a light back to the marriage so that the betraying spouse will see that the grass isn't necessarily greener. Doesn't sound like he's shining a very bright light. Maybe if you offered him a little more encouragement he'd do more? Not sure if you're in a place to offer encouragement.
You should do some reading, thinking, and talking to others. There's a lot on your plate right now. I really think you might benefit from the Glass book, though, to keep your friendship with OM in perspective.
And be warned - some LBS can feel a lot of resentment, so if one of us is rude to you or says mean things, please don't take it personally. We all benefit by having you participate in this forum!
