Starsky - that is good advice about boundaries, which I think DD should certainly use in "stage 2" (after building up the foundation of his improvements, and then confronting his wife at the right time).
Wouldn't DD then have laid an unstated position with his wayward wife of "I'm willing to live in an open marriage, because I haven't yet become a man worthy of your fidelity" ?
I will admit that I'm not too familiar with his sitch, but -- generally -- that is the main problem I have with the "I will lay out my boundary later" strategy. If a spouse is cheating, and their betrayed spouse KNOWS their cheating, and (stay with me now) the cheating spouse KNOWS that the betrayed spouse knows that they're cheating . . .
. . . and they do not lay an immediate "I am not willing to live in an open marriage" boundary . . .
. . . but rather just begin to work on themselves (I am in FAVOR of working on themselves, but only in conjunction with simultaneously stating their "I will not share my spouse with another person" boundary) . . .
then the betrayed spouse has basically said, by their (lack of) words and (lack of) actions, "I'm okay with this. At least until I've improved myself, because I've been a crappy spouse."
This is why I've never been a proponent of "only lay out your boundaries LATER, when you've made your improvements and when you're somehow "ready." To me, IMMEDIATELY (or at least a day or two after bomb drop, when you've had a chance to think thru what you're going to say and do) is absolutely the best time to do it.
Again, it all depends on what your non-negotiable "boundaries of personal integrity" ARE, to begin with. If you really are okay with it (your spouse living out an unrepentant affair basically right in front of you) for some period of time, then fine -- it's not my business to tell other people what THEIR boundaries ought to be. But I think it's disingenuous when people say (as they do so often on these forums!) "Oh make no mistake, my husband/wife knows EXACTLY where I stand, because I've said thus-and-such!" . . . while their actions show exactly the opposite.
That DB mantra of "Believe none of what they say, and only half of what they do" cuts both ways. A betrayed spouse's actions towards their wayward spouse -- or their lack thereof -- will speak far, far louder than any of their words.