What are the first-type slight indications that the fog/love/relationship w/OM might be coming to an end? I would be encouraged to see any sort of sign.
this is the last thing you should concern yourself with. your wife is in love with and living and sleeping with another man. terms like "fog" "alien abduction" "mid-life crisis" are just nice pretty ways to say you have been dumped.
if you can approach it with that in mind and realize it is probably for the best and there is nothing really to grieve over you can begin to attack this in a more productive manner.
Whats the best thing to do when someone dumps you? stop talking to them. forget about them. move on with your life in a positive direction. give yourself a month or two (30 - 60 days) of no contact. stop contacting them. ignore their calls and emails. do everything you can to move in the opposite direction from them, like a new job, new hobbies, new friends, in fact find yourself someone you are compatiable with (a buddy) for companionship and conversation.
when they contact you, and they will (noone likes to get dumped not even the cheaters), carry yourself in a manner that is remarkable and memorable. Because getting rid of your arguing, cheating, good-for-nothing-but-a-heart-ache lover was the best thing that could have ever happened to you.
Quit worrying about what they are doing. I will tell you honestly they are having fun, the best time of their life. Why, shouldnt you to? They are not stressing over love chemicals and co-dependecy conversations. Why are you? The sooner you stop the sooner you can get on enjoying your life.