A woman's diminished libido in a long-term relationship is partly due to her partner's own lessening of lust over time – and the idea that her partner is no longer choosing or chasing her, according to Marta Meana, a sex therapist who ties women's sexuality to narcissism. Being relentlessly desired often unlocks women's own desire, according to researchers. But according to Meana, striving for emotional closeness with a partner quashes the separateness required for lust. "Melding left no separation to span, no distance for a lover's drive to cross, no end point where the full force of that drive could be felt," she says.
At least one couple profiled in Bergner's book seems to get monogamy right. Despite sharing three jobs and as many kids, the duo talks candidly about their sex life. Even if Sophie, a baseball afficionado, occasionally fantasizes about the Yankees' Derek Jeter during sex, she says their union works. "We never stop admiring each other. I'll say, 'You got your hair cut; it looks great.' And he still tells me all the time how good I look," she says, and then shares what she calls one of his subtlest lines: "I love you in those jeans. Can I get in them?"
That ability to communicate openly is one of the key lessons of the book – along with the notion of "how culture shapes who we are," Bergner says.
Bergner says longtime couples continue to approach him on his book tour to explain that the strength of their relationship depends on free-flowing communication about sex and desire. He advises readers to follow suit and then to listen to their partners, "despite the feeling of fear, of trepidation, of feeling threatened."
In his own five-year-long relationship with his female partner, Bergner says his research has raised "all kinds of conversations." He adds: "That gives me some faith that the advice I just gave about having candid conversations can actually work."
[Read: How to Make Love Last.]