It was a cold morning in 1994 when Iris Krasnow decided to leave her husband. Together, they had four sons — a 3-year-old, a 2-year-old and 6-month-old twins. She’d recently quit a dream job writing celebrity profiles for a national wire service and was now caked in spit-up, with two babies strapped to her chest in a contraption that allowed them to breast-feed while she vacuumed.

“I despise my husband,” was her constant refrain as she became convinced she didn’t need him. Krasnow called her mother to discuss the decision.

“Don’t worry,” her mom replied. “I never liked him anyways.”

Krasnow is still married. That was as close as she’s come to divorcing her husband of 23 years. Not that she hasn’t been wracked with boredom, disgust, loathing and malaise throughout her marriage. She’s experienced all of that and details each phase with unabashed honesty in her new book, “The Secret Lives of Wives.”

Still, the American University professor’s intention isn’t to bash marriage, but to extol it by investigating what really keeps a decades-long commitment humming.

’The Secret Lives of Wives’ by Iris Krasnow. (Gotham Books/GOTHAM BOOKS)

“All we want to do as human beings . . . is to love and be loved and to feel worthy,” she says by phone from her home near Annapolis. “We want someone in our lives we can count on, who loves us back, that we can trust and who will go the distance with us.”

Krasnow, author of “Surrendering to Motherhood” and “Surrendering to Marriage,” which was a New York Times bestseller, traveled the country interviewing more than 200 women who had been married between 15 and 70 years.

Her subjects cross demographic lines and claim varying levels of satisfaction in their marriages, but the happiest wives have several common traits. They are serious about their commitments. For them, as Krasnow, puts it, “ ‘I do’ means, ‘I will, if I can,’ and not, ‘I might.’ ”

But they are not joined at the hip with their husbands and have friendships and interests outside their marriages. “In order to keep the promise, ‘till death do us part’ without killing someone first,” Krasnow writes, “ a woman must have work and hobbies she loves, extramarital adventures and a wine cellar.”

For several women Krasnow interviewed, “extramarital adventures” included affairs. But for most, it meant other passions: art, athletics, community service or spiritual development.

But many women lose sight of those interests, Krasnow says, especially those who spend decades defining themselves as “mommy.” These are the women who — like Krasnow — are facing the prospect of an empty nest. “Our fulfillment for so long comes from rearing our children,” says Krasnow, 57. “So the angst and the questions were, ‘How am I going to stay married to this same old husband in this different life?’ ”

The answer, she says, is to rediscover dormant passion and use this newfound time and freedom to explore it.

Iris Krasnow, author of ‘The Secret Lives of Wives.’ (Courtesy of Iris Krasnow/COURTESY OF IRIS KRASNOW)

The biggest commonality Krasnow found among women who are still satisfied after years of marriage is that “they never bought into the dangerous fantasy — the myth — of ‘Happily Ever After,’ ” she says. “That fantasy is a ticket to divorce, I think.”

“What I really wanted to do with this book,” says Krasnow, “is release all of us to realize there’s no gold-standard marriage toward which any of us should aspire.”

Back in 1994, as she contemplated divorce, the second phone call Krasnow made was to a sex therapist friend, who told her not to leave her marriage. The woman offered a piece of advice that Krasnow now passes along as the key to a good marriage: “Lower your expectations.”

“When you let go of the ‘Happily Ever After’ myth,” she says, “. . . you see that imperfection is all you can ever expect.”