I see divorce, often, as the result of our improved standard of living. Lots of people are just lousy to be married to (how many people do you meet about whom you've said not "Gosh, I'd love to go home with him for one night" but "Gosh, what a joy it would be to share a life and the flu and sunburn with that guy"?). When we were out in the fields or giving birth and raising the five kids (after three died in childbirth), we didn't have to spend much time with our spouses. For women, chances were pretty good that death would carry us off before our marriage reached its silver anniversary, and often before we reached tin. People did not sit around from Friday night to Monday morning looking for their spouse to fill the weekend with fun, intimacy, and sex. Rich people had numerous choices for all three, and poor people, as always, were just trying to keep the wolf from the door, which is a great wet blanket for fun, intimacy, and sex.
Despite all the slightly strange nationwide mourning for the innocence of the fifties (and you nine people who actually had the Ozzie and Harriet family and loved it, you go stand over there; the other 218 million, you go on reading), those years were the last gasp of widespread, middle-class, unambivalent segregation between the sexes. I know you don't see many fathers on the playgrounds on weekdays, but you do see some. And you see plenty of women catching the morning commuter train (they may have baby spit on their lapels and look insane, while their male counterparts are in spitless suits, reading the Times, but still...) and plenty of guys at their daughters' and girlfriends' soccer and rugby games on through college. The division of his turf/her turf that was so crystal clear (and so inimical to human development) has softened somewhat, which is mostly good news, but that blurring has taken away yet another way of having a good, if not happy, marriage; and without the cultural sealant of happy housewife and 9-to-5 warrior, it's become painfully easy to perceive the gaps and dissatisfactions and incompatibility.
It is the long but not happy marriage that breaks my heart: People who have slept in the same bed (or at least the same house) for 30 or 40 or 50 years and are, at best, decent roommates and considerate companions or, at worst, locked in a Strindbergian horror show, picking, bickering, and loathing each other, handcuffed to a life sentence, serving their time with a loneliness that transcends solitude.