Various complex theories abound on the reasons for nonconsensual extra­marital sex. In part, intrinsic conflicts in human nature contribute. As author Erica Jong explained, "We are pair-bonding creatures—like swans or geese. We can also be as promiscuous as baboons or bonobos. Those are the two extremes of human sexuality, and there are all gradations of chastity and sensuality in between" (2003, p. 48). Sometimes nonconsensual extramarital relationships are motivated simply by a desire for excitement and variety, even when an individual has no particular complaints about his or her marriage and even says the marriage is happy (Nelson, 2010; Straus, 2006). A recent study found that men who had a higher propensity for sexual excitement were more likely to have sex outside their relationships. This correlation was not found for women (Mark et al., 2011).

Often, the reason for outside involvements is the unavailability of sex within the marriage. A lengthy separation or a debilitating illness of one partner can leave one vulnerable to an affair. A partner’s disinterest or unwill­ingness to relate sexually can influence a person to look elsewhere for sexual fulfillment. A recent study found that sexual incompatibility was a stronger predictor of sexual affairs for women than for men (Mark et al., 2011).

In other cases, people are highly dissatisfied with their marriages. If emo­tional and sexual needs are not being met within the marriage, having an affair may seem particularly inviting. Affairs in which emotional involvement is strong have been shown to be related to dissatisfaction with the primary relationship prior to the affair to a greater degree than have affairs with low emotional involvement. Affairs with strong emotional involvement are also more likely to lead to divorce (Allen & Rhoades, 2008). Recent research has found that women are more likely to have affairs when they are unhappy in their relationship, whereas this correlation was not found with men (Mark et al., 2011). In some situations, affairs also provide the impetus to end a marriage that is no longer satisfying.

A study of couples in marital therapy found several differences between couples in which infidelity was occurring and couples in which it was not. Couples in which it was occurring had more marital instability, dishonesty, arguments about trust, self – centeredness, and time spent apart (Atkins et al., 2005). The important question to ask about these negative marital characteristics is which came first—the dissatisfaction or the infidelity? It is just as possible for the dissatisfaction to have increased because of the infidelity as for the dissatisfaction to have motivated the infidelity. The person having the affair may treat his or her spouse differently due to feelings of guilt or to comparing the marriage with the excitement of the new relationship.

Living circumstances can play a role in regard to sexual exclusivity. When individu­als have weak ties to their spouse’s friends, family, and activities and are not involved in a religious community, the chances are greater of having affairs (Ali & Miller, 2004). People are more likely to be unfaithful if they have greater access to potential partners at work, through out-of-town travel, or simply by living among many people in the rela­tive anonymity of a large city. The increased number of women in the workforce may account in large part for the increased number of women having affairs (Carollo, 2011).

In the United States, we are accustomed to media headlines about prominent men being discovered having affairs. The lack of women in the same predicament creates the impression that many more men than women are unfaithful in their marriages. How­ever, recent research findings suggest that power may be a stronger predictor of infidel­ity than gender. An anonymous online survey of over 1,500 people by a prestigious business magazine found that men and women who were in top positions of power in their professions were equally likely to have had affairs and to be considering them in the future. These men and women were also much more likely to have had affairs, and to have had more affairs, than people who had less power in their professional lives. The gender imbalance in media headlines may be due to the fact that fewer women than men are in positions of power (Lammers et al., 2011).