We prefer honesty in our relationships, but reality doesn't always measure up to our expectations. Cheating is an everyday occurrence. Some cheating isn't even considered cheating. Football games are won by trick plays and earn quarterbacks the title of hero, along with multimilliondollar salaries. Other cheating is entertaining, like the magician's repertoire of card tricks, sleight of hand, and beautiful women who disappear or survive being sawed in half. Military strategy often involves camouflage, which throughout history has won wars, going back to the Trojan horse in ancient Greece.

Most cheating however is undesirable, whether it's a gambler trying to beat the casino, the student who cheats on exams, the citizen who fudges numbers on a tax return, or the CEO who pays himself a multimilliondollar bonus while shareholder profits plummet. But perhaps the most disappointing, and personally painful, cheating is that which occurs among lovers and spouses. An unwritten expectation of fidelity is the core of our sexual relationships. We expect our partners not to cheat. Sometimes lovers release each other from that expectation, as in the 1960s and '70s when ''open'' relationships and ''free love'' were part of a sexual revolution that valued experimentation. The vogue continues to a much lesser degree in the twenty-first century. For the most part, when two people are in a committed relationship, monogamy is not only implied, it's assumed. One mate at a time is the expectation when you've given your heart and soul to another.