I've just finished reading most of this thread, and I hate to tell you this, but your life sounds so much like mine, it's spooky! Except I've got 15 years and 2 more kids on you.
Question about your sitch: how long had it been since the previous last ML session? Sorry, I'm still getting caught up here - I haven't been here for most of the past year.
For me, the past 10-15 years have been long deserts of 3-8 months, with brief oases here and there. There have been "dry" periods of over a year at times.
I, too, read the LRT post when I read Monk's thread. That was one of the things that led me to my "letting go" feeling that this next attempt at getting things (back) on track will be the last. If it doesn't work, then the end-game goes into effect.
In my family, divorce is almost unknown, but my youngest sister just separated from her husband, with a young DD (8-10yo?). Sorry, but I'm firmly with Doctor Laura on this one... kids need to be in a family until they're old enough to handle the breakup, which is (in my mind) almost grown. Yeah, if my W and I split when our youngest is 15, I'll feel like I'm fudging that one a bit, but eventually we do have to take care of ourselves. I do think that by that age he'll be able to get through it. Yes, it'll affect him, and probably greatly, but I'm hoping it won't destroy him at that point. If I took that road now, I'm sure it would. That is something you will have to think very clearly about, concerning D6. I won't pretend to put any attitude on you, but you'll need to keep her very clearly in mind, and your eyes wide open. Even a "dead" marriage is a better environment for a child than a broken one. Believe me, I know where you're at right now... been there, and have a closet full of tee-shirts...