I rarely agree with Froma Harrop’s politics but she has a very perceptive editorial on what makes long-term marriages happen:

You know the quip: A wife is asked on her silver anniversary whether she has ever contemplated divorce. “Divorce, never,” she replies. “Murder, frequently.”
That sums up the truth about long-term marriages. Their success doesn’t rely on everybody’s being compatible or happy or a champ in the sack. The people who stay married are the people who won’t consider divorce.
This sounds circular, I know, but it’s the case…For the moment that divorce becomes a card on the table, there will be a temptation to play it…
…when a spouse blows up with rage — and the best of us do — true commitment is the only glue that can hold things together…
Several states have passed laws letting couples opt for a stricter kind of union, called a covenant marriage…
But what can withstand the modern love of freedom? An unhappy partner can get out of covenant marriage quicker than Houdini could pick the lock on a piggy bank…
Marriage counseling, meanwhile, can do only so much. By the time the angry couple decides to hire a therapist, it’s usually too late…
And in going through the reasons for discontent, therapists often unwittingly add fuel to the fire…Therapy can take lots of little stuff and roll it into one big unhappy ending…
But for the person truly dedicated to staying married, the answer is somewhat different. It is “I don’t want to spend the next 30 years living like this, but I’m going to do it anyway.”
People marry for different reasons now than they did two generations ago, which helps account for today’s higher divorce rates. Marriage used to be about economics and child rearing, according to David Popenoe, co-director of the National Marriage Project, at Rutgers University. Now it’s a love-based decision….
Finding money for new wallpaper is not impossible. But re-creating That Old Black Magic month after month is. After a while, the flame of passion dims into an occasional spark, if the couple is lucky. And restoring it is beyond the powers of Shakespeare, Dr. Phil or Barry White.
…according to Popenoe…[h]is studies show that marriages today are, if anything, a bit less happy than they were 20 or 30 years ago. Work stress is a big reason.
But this is not necessarily bad news for couples struggling to stay together. Sometimes it helps knowing that one is not supposed to be happy all the time.
Two dear friends recently marked their 55th anniversary. I asked the husband whether they ever wanted to strangle one another. He said, “Yes, like last night.” But they’re married for life, and that’s it.
The couple that stays together is the couple that stays together.

Food for thought, isn’t it?