The New York Times carries Ira Glass’s account of his psychologist-mother’s life, the “Doctor of Daillance” who studied extramarital affairs (excerpt):
What she discovered in those first surveys was later confirmed in her work with the hundreds of couples she counseled: when a person cheats, it doesn’t mean there’s a problem in the marriage. Over half of the men and a third of the women who had had affairs said they were happy with their spouses.
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But to her, an affair was more like a medical condition: it followed predictable rules and was perfectly preventable, if you recognized the early signs. Sadly, not many people did. As more women made it into the workplace as equals with men, more than half of the affairs my mom encountered started on the job. Women and men in happy marriages, not intending to cheat, got close to someone at work, sharing confidences and intimacies, until they fell in love. The cheating spouses sometimes seemed as confused as their partners at how it happened.
When had they crossed the line? Not when they finally kissed, my mom said. In a sense the sex was just the endgame. They crossed the line when the married person began confiding in the friend at work. When you entrust what you really think to someone outside the marriage, when your friend knows more about your marriage than your spouse knows about your friend, you’ve gone too far.