I am in the same boat as you are my friend. What a mess.
Here is something that I found that seems to provide some clarity at least for me. It does not help me any but it is the best explanation I have found.
Now let us consider the other gender: is there a pattern to be found among women in their decision to get divorced? Yes, in fact there is an unmistakable and almost invariable profile of women who choose divorce. They are in their 30s; their husbands, by the wives' own description, are decent guys; they have young kids; and, almost invariably, they have a boyfriend.
Every day I meet with a man in his 30s whose wife wants a divorce. My client is usually stunned and confused. His wife is sending mixed signals, and her reasons for wanting a divorce are vague. She even seems, at times at least, ambivalent as to whether she wants the divorce. My client desperately wants to save the marriage. His tendency is to blame himself and to irrationally focus on his deficiencies as a husband. He tends to cling to her (in effect if not in fact), repeatedly asking for another chance. He pathetically assures her he will do better. If I ask him what exactly there is for him to do better, he commences an anguished recital of a much-considered and lengthy list of his spousal failings. As I listen, I realize these items cannot, even cumulatively, explain his wife's decision.
What my client does not yet realize, however, is that his wife's decision to surrender her family has nothing to do with him. I believe the stimulus is something much deeper. The fact is that women in their 30s are intensely conscious of aging. You do not have to have a Ph.D. in sociology to realize that the fact of aging is of more importance and urgency to your wife than it is to you. Women in this culture (perhaps in all cultures) have not failed to notice that physical and sexual attractiveness are powerful and frequently determinate factors in their relationships with men. Therefore there is a closing window of opportunity for women in their 30s to obtain a desirable mate. For married women this means a lateral move or, better still, the opportunity to trade up. Put differently, the cement is drying. If such a woman is not completely "fulfilled" (whatever that means), she must take steps soon, if ever, to rectify the situation.