Some women feel that they are the emotional support for the entire relationship and are burdened with most of the work. As their needs go unmet, they build a lot of resentment towards the husband and once the wall of resentment is too high to cross, there is little the man can do to fix the issue. Men typically use the word divorce as a warning sign, women use the word divorce because they are done. Once again, failure to communicate is a vital key. Women expect their husbands to "know" what they want. Men are in their own world thinking all is well.
Having gone through this and suddenly seen it everywhere, I have to kinda agree, but mainly disagree. I think what happens to women is, in the nutshell version, as young girls they are expected to be the second mom in the family, sometimes even taking care of their own mom who may have drug and alcohol problems. So they grow up being almost the primary caregiver in the family and the first thing they do when the grow up is go off and start their family. At that point though, they're either uncapable of accepting love and support or they just don't see it, because they never experienced it growing up.
Speaking for myself, I put my xw on a pedestal and there wasn't anything I wouldn't have done for her and I bet a lot of guys that were in my situation did the same thing, which may not have been a good thing as it kept the blinders pretty firmly in place. I digress, but it's quite confusing when these women run away from great guys only to start all over, somewhere else.
I think this is why: they've been unfairly burdened their whole lives by their own families and it doesn't matter how good of a husband / father / guy he is, the woman has it built up in her head that she's the victim to the point that nothing is going to convince her otherwise that her contribution, sacrifice and suffering was greater than that of her husband. That's probably the first thing everyone tells the OP.. how bad they have it.
Like I said, once I went through it I saw it everywhere, however, it's also something men don't talk about openly. Facebook is full of posts from women about "girls.. you know how guys always", but none are from guys who went to work, came home, turned over his paycheck to his wife, never had time for his own hobbies or friends, always spent time with his kids and his wife dumped him because he was a "loser".
Anyway.. just for the sake of friendly conversation, I wouldn't assume a woman's needs were unmet. It happens, but if a woman is mature and confident, I think the chances are she either waits until the kids graduate high school before getting a divorce or it's more of what we would call a walk away spouse and they wouldn't jump right into another relationship while they were still living with their family.