If there's anything fundamental to the meaning of marriage in Western society, it's monogamy. In fact, monogamy may be the only thing that remains essential to most people's idea of marriage. People no longer marry for economic, dynastic, or procreative reasons, as they did for millennia; they can't be compelled to marry by law, religion, or custom; they don't need to marry to have sex or cohabit or even produce and raise children. But throughout all of this staggering change, the requirement and expectation of monogamy as the emotional glue that keeps the whole structure of marriage from collapsing under its own weight has remained constant.
Given the almost universal public denunciation and disapproval of infidelity (which doesn't exclude the barely hidden schadenfreude at the deliciously scandalous goings-on of celebrities, famous preachers, major political figures, sports heroes, or even your office coworker caught in flagrante), you'd think that infidelity must be quite rare. At least nice people don't do it—we wouldn't do it.
Except that we would and we do—much more than most people seem to realize. As a culture committed, in theory, to monogamy, our actions tell a different story. It isn't just that, as therapists, we need to understand that infidelity happens—we all know that already. What some of us may not realize is how often it happens. Research varies, but according to some surveys, such as those reported by Joan Atwood and Limor Schwartz in the 2002 Journal of Couple & Relationship Therapy, 55 percent of married women and 65 percent of married men report being unfaithful at some point in their marriage. Up to one-half of married women have at least one lover after they're married and before the age of 40.
If these surveys are correct, the high incidence of infidelity isn't because we live in a particularly licentious, amoral age—the public jeremiads of religious scolds notwithstanding. According to noted anthropologist and researcher Helen Fisher, extramarital affairs have always happened at this high rate, but only now are we getting a more accurate, statistically informed, picture of what's going on. Fisher also reports that what you might call this "state of affairs" holds true across at least five other cultures worldwide that she's studied.
Within our profession, virtually all couples therapists, whatever their model—psychodynamic, systems, behavioral, insight-oriented, solution-focused—have believed since the field's earliest days that no troubled marriage can recover as long as there's a "third party" hovering in the wings. Ongoing infidelity, however defined—sexual, emotional, physical, "cyber"—is, for most therapists, an automatic deal-breaker to meaningful therapy, not to mention clinical improvement in the marriage.
One major impediment to the view that an affair indicates that something is profoundly wrong in the marriage, however, is that 35 to 55 percent of people having affairs report they were happy in their marriage at the time of their infidelity. They also report good sex and rewarding family lives. So how can we continue viewing affairs as symptoms of dysfunctional marriages when apparently so many of them seem to happen to otherwise "normal," even happy couples? The one-size-fits-all view of infidelity never questions the standard model of monogamy, much less helps a couple explore a new model of monogamy that might work better for them and their own particular marriage. Furthermore, a therapist who takes sides, implicitly vilifying one partner as "bad," endorsing the other as "good," is much likelier to lose the couple early on, since infidelity is rarely a black-and-white issue.