>>It's like when he's pressured, he's certain D is the answer. Otherwise, everything is great and wonderful just as it... <<
I think the reason he feels D is the answer is because this problem just seems too big and overwhelming to work though. D seems like the easiest answer. And in some ways you have been agreeing with this. Neither of you are convinced you can make it through this.
>>he is most comfortable with leaving his family to start up a new life with someone who he has built a relationship with that is based on lies and deceit.<<
He probably feels the only thingl he's good for at this point is a "screwed up" relationship. She's the default if the marriage fails. She'll be the rebound. Unhealthy maybe, but a temporary resting place while he tries to get his head together.
>>When left unchallenged, he prefers to go along as is.. << He still needs the quiet and space to figure things out. And I don't think he wants to lose his family, but he knows he has done so much damage, and he thinks, maybe you guys will never recover.
There is no arriving, ever. It is all a continual becoming.