I guess I'm still unclear on this "not working for me" talk would need to be like. Every time I work on that, it sounds like an ultimatum. How is this different?
It's only an ultimatum if she believes it's just a tactic to win her back. You have to REALLY be of the mind that "you know what? this ISN'T working for me! I deserve better than this, and I don't want to beg someone to be with me!" If you really mean it, and just let her know "I've heard you, you don't want to be married anymore and this isn't working for me either, so why don't we just move on" is in NO WAY an ultimatum.
As men, we have a really hard time with the whole "letting go" thing, because we're fixers and control freaks by nature. But when you fully realize that YOUR WIFE IS NOT YOURS TO BEGIN WITH, AND YOU CANNOT CONTROL HER . . . you will be 75% of the way toward successful DBing.
Are you familiar with the "you're already dead" scene from Band of Brothers, or the Stockdale Paradox? Both are based on this same concept. Powerful stuff.