Ask anyone what they think keeps a relationship strong, and they will probably tell you it's love. There's some truth to that: love is what draws us together in the first place. But after years of studying couples as a psychologist, and as a husband, I've realized something that research keeps confirming: The real factor that keeps couples together, long after the honeymoon phase fades, is compromise. Psychologists define love as an emotion. And like all emotions, love fluctuates with stress,