There is no agreement over how honestly we should discuss this reality with our own spouses. Some are nostalgic for the old hypocrisy, the code of silence, the mistresses and concubines men kept discreetly on the side. Clergy members may practice a kind of selective muteness: in their premarital counseling, they often do not stress the possibility of future affairs — but once an affair occurs, they vocally urge couples to tough it out. But what if they were to say, ahead of time: “You two love each other, and you promise you won’t stray, but you might. People do. And if you do, I hope you won’t think it’s the end of the world.”

Such straight talk about the difficulty of monogamy, Savage argues, is simply good sense. People who are eager to cheat need to be honest with their partners, but people who think they would never cheat need honesty even more. “The point,” he wrote on his blog last year, “is that people — particularly those who value monogamy — need to understand why being monogamous is so much harder than they’ve been led to believe.”

How exactly does Savage think talking about monogamy’s trials make practicing it easier? In part, by reminding people to be good, giving and game. Straight talk about why we might cheat helps couples figure out ways to keep each other satisfied at home. If I promise my wife that I would never, ever, ever sleep with another woman, the conversation might end there, the two of us gazing into each other’s eyes (even if our minds might be wandering). But if I say, “I’ve been feeling sexually unfulfilled lately because I have a secret fantasy about trading dirty pictures with a woman” — well, then maybe my wife will e-mail me some of her. And so monogamy is preserved.

“If you are expected to be monogamous and have one person be all things sexually for you, then you have to be whores for each other,” Savage says. “You have to be up for anything.”

Savage’s straight-talk approach has an intuitive appeal: our culture places a huge premium on honesty, or at least on confessional, therapeutic, Oprah-fied admissions. We are told to say what is on our minds, so why not extend that principle to sex? Why not tell your spouse everything you want, even if that includes wanting another person? My sense is that this kind of radical honesty may work best for couples who already have strong marriages. Where there is love and equality and no history of betrayal, one partner asking if she can have a fling may not be so risky. Her partner either says yes, and it happens, you hope, with only the best consequences; or the partner says no, in which case their relationship endures, maybe with a little disappointment on one side, a little suspicion on the other.

That is the ideal situation. What if the revelation that a partner is thinking about others creates a shift, one that plagues the marriage? Words have consequences, and most couples, knowing that jealousy is real and can beset any of us, opt for a tacit code of reticence. Not just about sex but about all sorts of things: there are couples who can express opinions about each other’s clothing choices or cooking or taste in movies, and there are couples who cannot. I don’t mind if my wife tells me another man is hot, but it took me a long time to accept her criticism of my writing. We all have many sensitive spots, but one of the most universal is the fear of not being everything to your partner — the fear, in other words, that she might find somebody worthier. It is the fear of being alone.

Where a relationship is troubled, and one partner senses, correctly, that aloneness is an imminent threat, then the other partner asking for permission to have a fling is no neutral act. If you are scared of losing your partner, you may say yes to anything she asks, including permission for an affair that will wound you deeply. “The problem is that with many of these couples, one partner wants it, and the other says yes because she’s afraid that he will leave her,” says Janis Abrahms Spring, a psychologist and couples’ therapist whose book, “After the Affair,” is about couples badly damaged by infidelity.