Another conversation yesterday - interesting twists. My son and I were "camping" in the back yard, and she came over and spent some time with us at the fire. She was walking around the property, kind of wistfully looking at things, and talked about how I would continue on with some building plans we had together.
Back in the house, she and I talked a little more about past issues, and present. She told me that where I neglected her, the OM is clingy and "smothers" her - but of course, said that he apoligized and backed off when she lost her cool about it. She's a pretty solitary person when working through things, and he and three 4-6 yr old boys in the house aren't going to be comfortable for her. I tried to draw out where she was going with the complaints, but she wasn't saying more. She really seems to want to be alone, but feels like this OM is her way out - not that she doesn't have feelings for him, it's just that her expectations aren't as "sky-high" as some here would think.
The other part of the conversation was her volunteering what a big part she's had in our problems - her own depression, irritability, and cruel comments that angered me, pushed me away, and contributed to my depression issues.

She noted several times that she's not the same person she was - I told her that was great, I'm not either, and that is why I see hope for our future - we COULDN'T stay the same and survive. I can tell you, though, that her changes aren't all positive - she's still not recognizing her impact on others - in a way, she's become more selfish, not less, but I think that's part of learning to be independent - not as easily hurt by minor things. A kind of strength, really.
Strange conversation - she didn't want to have it - I believe it makes her falter in her resolve to vacate the marriage, house, etc., just as seeing my son and I together does. On the other hand, she always talks to me before she "wakes up" and ends the thing - like she wants to, but thinks it's a bad idea.
Oh well - another day, another challenge.
Thanks for your help, NC - I can see some really good advice and a lot of strength from you. Good luck with your own relationship!