David Brooks writes that your marriage is the most important factor influencing if you are happy or not:
Marital happiness is far more important than anything else in determining personal well-being. If you have a successful marriage, it doesn’t matter how many professional setbacks you endure, you will be reasonably happy. If you have an unsuccessful marriage, it doesn’t matter how many career triumphs you record, you will remain significantly unfulfilled.
This isn’t just sermonizing. This is the age of research, so there’s data to back this up. ... one of the key findings is that, just as the old sages predicted, worldly success has shallow roots while interpersonal bonds permeate through and through.
Andrew Sullivan points out that this fact makes gay marriage bans even more cruel:
Now imagine the government actively prevents you from marrying the one you love, and having the stability and support and love and friendship that make life worth living?
While we're at it, take a look at
Jonah Lehrer's explaination of what makes a successful marriage:
...I'm mostly convinced that there's a fundamental mismatch between the emotional state we expect to feel for a potential spouse - we want to "fall wildly in love," experiencing that ecstatic stew of passion, desire, altruism, jealousy, etc - and the emotional state that actually determines a successful marriage over time.
Berscheid defines this more important emotion as "companionate love" or "the affection we feel for those with whom our lives are deeply intertwined." Jonathan Haidt, a social psychologist at the University of Virginia, compares this steady emotion which grows over time to its unsteady (but sexier and more cinematic) precursor: "If the metaphor for passionate love is fire, the metaphor for companionate love is vines growing, intertwining, and gradually binding two people together."