I've followed your sitch for a while now and I also have alot of admiration and respect for you. I, too, waver from day to day, thinking .....I am done with this man (and I use the term loosely); let's have some fun with his idiocy. Then I realize that using my H for amusement purposes will not result in what I ultimately want. (although I am not sure WHAT it is I want these days).
My H also says he is done. I think, at most, he was having an EA at the time he left, although the OW did not surface (to my knowldege, at least, til after he was gone about 2 months)....
It's sort of like, which came fist the chicken or the egg (the OW or the MLC)? Like you, I can't find too much written about OW's AFTER the H moves out.
I think both situations involve the H feeling he is entitled to his A. And I'm not sure it really makes a difference when the OW comes into the picture. I do, however, know that whether or not H is still married (by law), he considers himself to be "single".