There is no sex without a cue. People who date have their cues at home, before they meet. You think about where to go, what to eat, what to do and say. Sometimes the cue is short - - just before we reach the bar - - but sex is never just spontaneous. Spontaneity is a myth.

As a teenager growing up in Europe, I embraced the romantic ideal. For me, I had to give up the ideal that one person would be there for everything. Once you give up that ideal, then you begin to accept the person that you are with - the person who won't be able to give you everything and who won't be able to know exactly what you want and feel without you even needing to say it.

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.

Affairs can be powerful detonators. They can invigorate a marriage that's flat, jolt people out of years of complacency. Fear of loss rekindles desire, makes people have conversations they haven't had in years, takes them out of their contrived illusion of safety.

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.

In desire, there must be some small amount of tension. And that tension comes with the unknown, the unpredictable. You can close yourself off at home and say, "Whew, at last I'm in a place where I don't have to worry," or you can keep yourself open to the mystery and elusiveness of your partner.

Marriage isn't meant to make you happy - it's there because it gives you a life in which you can find happiness.