The attraction of dating is that you don't take yes for granted - - you're fully engaged, there's seductiveness, tension.

Today, monogamy is one person at a time.

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.

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.

The mom doesn't become sexy; the woman does. You have to retrieve the woman from the mother. And she may need to separate to do that: a bath, a walk. She must cordon off an erotic space.

The one word I hear when people have affairs is that they feel alive. They don't talk about the fact they're having sex. They feel like they are engaged with their life. They describe an experience that beats back the deadness inside, which isn't the fault of the marriage or the partner. It's often the deadness that they have allowed to creep in for years on their own. But by definition, it's a transgressive act. And transgression is a breaking of the rules. And it gives you a sense of ownership and freedom. And ownership and freedom gives you a feeling of aliveness. It's a chain.

For most couples who come to me - especially in the aftermath of the revelation of an affair, when they are in a state of crisis and fear the loss of a predictable future - they start to have conversations for the first time about love, sex, monogamy, and marriage. Most couples don't negotiate or don't even converse about any of these things until the crisis of the affair has actually forced them to. Why does it take infidelity to get us talking about the stuff that should be there from the start?