Some stats

Monogamy is something most people often say they believe in and want for themselves. Every survey ever done on this question shows a high percentage of people think that monogamy is important to marriage and that affairs are wrong. And most people, when they marry, "intend" to be monogamous. But a belief in monogamy as an ideal doesn't prevent large numbers of people from having extramarital affairs.

Those who have looked at a wide range of studies recognise the "myth" of believing that most people are monogamous. Here are some statistics based not on any one specific study, but on what the 'general consensus' of researchers who have studied this issue is:

According to Annette Lawson, author of "Adultery":

"The various researchers arrive at a consensus .... suggesting that above one-quarter to one-half of married women have at least one lover after they are married in any given marriage. Married men still stray more often than married women- perhaps some 50-65% by the age of 40.

According to Peggy Vaughan, author of "The Monogamy Myth":

"Conservative estimates are that 60% of men and 40% of women will have an extramarital affair. These figures are even more significant when we consider the total number of marriages involved, since it is unlikely that all the men and women having affairs are unlikely to be married to each other. If even half of the women having affairs ( or 20%) are married to men not included in the 60% having affairs, then at least one partner will have an affair in approximately 80% of all marriages. With this many marriages affected, it's unreasonable to think affairs are due only to failures and shortcomings of individual husbands or wives."

Note that the above assessments of the prevalence of affairs were made about a decade ago; so based on changes in society during the intervening years, the current percentage of the population who have had affairs is probably somewhat higher. For instance, the continuing increase of women having affairs on the internet means that the number of women having affairs is probably similar to men - about 60%

The effect of believing that most marriages or committed relationships are monogamous is that if an affair happens, it's seen strictly as a personal issue requiring 'therapy' for the individual who failed to be monogamous.