Infidelity

Infidelity is a breach of trust that signifies a lack of faithfulness to a moral obligation to one's partner. Infidelity usually implies sexual infidelity, although some people, particularly women, regard an intense emotional relationship as an unfaithful extramarital involvement, even when there is no physical component. In short, infidelity is feelings or behavior that go against a partner's expectations for the exclusivity of the relationship. Some couples are comfortable with having relationships outside their union. These liaisons do not constitute infidelity unless they violate the couple's shared understandings about discretion, partner choice, and sexual conduct—understandings that are designed to protect their relationship from disruption.

In the United States, open marriages that tolerate extramarital sex are the exception. Most U.S. husbands and wives say that sexual fidelity is very important to a marriage (Blumstein and Schwartz 1983; Greeley 1991). Ninety-nine percent of married people in the United States say that they expect sexual exclusivity of their spouse, and 99 percent report their spouse expects the same of them (Treas and Giesen 2000). Cohabitors are only slightly less likely (94%) to say they expect fidelity from a partner. Although males in same-sex couples tend to be more tolerant of multiple sexual partners, few heterosexuals in the United States are indifferent to their mate's sexual activities.