For some people, a one-night stand doesn't make any difference in a seven-year love affair. I don't believe the degree of betrayal is always commensurate with the egregiousness of the behavior. They are two separate things.

On some level we trade passion for security, that's trading one illusion for another. It's a matter of degree. We can't live in constant fear, but we can't live without any. The fear of loss is essential to love.

You know what happens to sex in marriage? Instead of inviting desire, you monitor it. Especially men: You let her sleep late, you take the kids to the park, and all that time you're thinking, "Tonight I'll get some." That doesn't work.

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?

To look at infidelity from the point of view of sex is a complete narrowing of the phenomenon. There's a reason that the commandment is repeated twice in the Bible - once for doing it and once for thinking about it. We have always created structures and broken structures. It is essential to the human spirit.

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.

For me, the constitutive element of an affair is the secrecy. It is the secrecy that leads to the lying, to the deception, to the duplicity. It is the structure of an affair - not the sexual or emotional behavior or what people actually are doing.