There is not one person who can fulfill all your needs. You may choose a partner who is your intellectual equal, and he may not be your most compatible sexual partner. And then there's the duality between security and adventure. A relationship that gives you plenty of novelty, and adventure, may not provide the stability you long for. Time, continuity and familiarity with somebody gives you other things in life but won't necessarily give you the kind of intense lustful experiences that you may have when you first meet someone and are curious about penetrating the mystery of them.

Many couples have never had a conversation about sexuality and sexual boundaries. The presence or lack of sex, the quality of it, the satisfaction and dissatisfaction, the unmet needs. An affair upsets the status quo by not only bringing the subject of sexuality to the forefront but every other aspect of their relationship as well. An affair yields conversation that should have happened in the beginning, but that people were afraid to have because, well, what would that mean about their relationship?

A peer relationship is one where the partners experience an affectionate, companionate coupledom. They are friends. They are the product of the egalitarian model; they are good life partners, but are often less sexual.

The very ingredients that nurture love - mutuality, reciprocity, protection, worry, responsibility for the other - are sometimes the very ingredients that stifle desire.

In committed sex, in marriage, people don't feel the need to seduce or to build anticipation - - that's an effort they think they no longer need to do now that they have conquered their partner. If they're in the mood, their partner should be too.

Secrecy fuels erotic intensity because it makes you feel like you're doing something that is entirely yours. It gives you the sense of autonomy, the sense of freedom, and the sense of sovereignty. And then you add to that the sexual energy. In many affairs, people will tell you they slept with the person three or four times, but the story went on for months. That's an important thing because many people who have affairs often have very good sexual relationships at home. It's not necessarily a compensation story. But affairs offer a different sexuality with a different context.

At this point, we are living one of the greatest experiments in humankind - to create something that has, throughout history, been considered a contradiction in terms - a passionate marriage. Passion has always existed, but it took place somewhere else. Everything that we wanted from a traditional marriage - companionship, family, children, economic support, a best friend, a passionate lover, a trusted confidante, an intellectual equal - we are asking from one person what an entire village once provided. And couples are crumbling under the weight of so much expectation.