I kind of hate to say anything; I sense your exhaustion with the situation. I wish there were something I could suggest that would ease your burdens. Unfortunately I think you're locked in a real impasse, and the situation is likely to persist (with minor variations) as long as you allow it to.
The "act as if", detachment approach helps you maintain your own sanity, keep yourself looking as attractive as possible, and maybe find some space for personal growth. Whether by itself it works in the end to rebuild your marriage into something good depends on your spouse's response, whether the disenchantment or misbehavior was a passing period of "temporary insanity" in an otherwise mature person, or a manifestation of their basic personality. People who are stable enough to be worth marrying (and staying married to) know how to be happy and cherish others. People who have too much chaos within them don't.
It's great that you've given your wife so much time and space to find her own way out of her labyrinth. But if it hasn't happened by now, it isn't likely to. Something I've observed in most situations of long-term marital discord is what I'd call limit-seeking behavior, where one or both spouses seem to have developed an innate sense of the limits of the endurance of the other, and continually push the envelope right to that point. And I've seen these situations go on for year after year and decade after decade. My in-laws would make an interesting case study.
At what point, after giving her all this time and space without meaningful improvement on her part, does your behavior amount to enabling? As time continues to pass, she piles up more bad actions and the burden of your resentment can only grow. I've been kind of a slow learner myself. It took more than a few lessons, but my wife finally taught me that she would treat me just as badly as I allowed her to. Once I realized that she wasn't going to figure it out on her own or learn by example, I just stopped tolerating anything I considered unreasonable. That actually has sort of worked.
