Love has very little to do with a happy marriage contrary to the romantic myths in our society.
Marriage is about committment, not love. We can love a lot of different people but we can't marry them all. Love, when it comes to marriage, is a decision, not a feeling.
Marriage has to do with reliability, dependability, trust, honesty, companionship, understanding, empathy, respect, loyalty.
If you want to know the kind of people not well suited for marriage, get a hold of the DSM-IV, the Diagnostic and Statistical Manual of the American Psychiatric Association, and read the section on "Personality Disorders". My advice is, in general, if you want to be happily married, don't marry somebody with a personality disorder, and yet people do it all the time and then wonder what went wrong to their love.
One of the biggest tragedies in life, and we rarely talk about it, is to marry somebody who isn't any good for you. It happens all the time. Over 50% of the time. If people were more aware, wiser, smarter, and didn't buy the notion that love is all there is to marraige, is the gold test standard for marriage, we would have far fewer divorces.
Love is nice. It is the icing on the cake, but not the cake. When love fades, when love fails, what's left? The traditional marriage vows say, "for better and for worse; in good times and bad; in health and sickness; for richer or poorer, til death do us part." How does marriage survive the worse, the bad, sickness, poorer when your spouse is an idiot?
Love in marriage is like the tide of the ocean, it comes in and goes out. Love in marriage is like the phases of the moon, it waxes and wanes.
Tina Turner had it right when she sang her great song, "What's love got to do with it. It's just a second hand emotion." There has to be a lot more to marriage than love.
Tina Turner, What's Love Got To Do It? Video lasts 3:44