In the conventional model of love, sexual desire and nonsexual intimacy go hand in hand. Gentle, automatic touches, the secret shared language of baby talk and pet names, unwavering emotional support—-all of these are signs of a loving closeness that we feel should fuel desire. And for many couples, it does.

But some long-term couples report stagnation in their sex lives, even as their sense of nonsexual intimacy grows stronger. They're having less sex—or no sex at all—though they cuddle often, spend every free moment together and love each other more than ever.

So what is to blame when couples say they feel more like best friends or roommates than lovers? Are they simply getting bored of sex with the same person, or could the closeness they've cultivated over the years itself be the culprit?

Cultivating loving separateness

In her international bestseller "Mating in Captivity," psychotherapist Esther Perel examines why sexual desire diminishes in certain long-term domestic relationships