Thanks Pam, your advice does help. I am quite a rational person, and I do have some clear goals regarding this marriage. I know that confronting OM may not achieve those goals, and may actually sabotage them; but the desire to do so is/was certainly strong.
Now, as of today, things have changed yet again as my unpredictable W came up with a new plan last night. Now she wants to live together "as friends/roommates" and she wants to go to Europe twice a year on vacation to spend time with the OM, "as friends." As ridiculous as this sounds, it is one step closer to the goal.
I didn't rant and rave, but listened and offered support for the idea. Now W is feeling very happy towards me, and is feeling some liking returning. We are flying off to Bali in a few hours for a week of relaxing without the kids. Wish us luck.