Interesting thread. I think affairs can fizzle out but with a MLC that can take years or never happen since the MLCer has no courage or strength to change things in his life.
My H and OW are 5 years together. In theory, limerance should be over by now. I have heard that they fight a lot. I know that they have broken up and gotten back together several times. They live in different countries, which I think suits my MLCer and probably keeps the relationship exciting. Then again, if two people are in love, doesn't one of them move to their love's country and be with them full time? If you're in love, you just want to be with that person, no? So there's something not quite right between H and OW.
Once when H and OW broke up, he told his L that OW was crazy. A week later, he was off to OW land to be with her. I believe my H is in a such a mess financially and emotionally that he could be persuaded by OW to marry her, especially if H should no longer have enough money to rent a place here and fly back and forth. Right now, we're not divorced so he can't marry her. One day, who knows. I don't put it past him, but I'm certain it will be a marriage from hell if he does.