According to Professor Steven Reiss, one of the most significant applications of the Reiss Motivation Profile® (RMP) is understanding relationships including romantic relationships. Below is an excerpt from a blog in which he shared his thoughts on infidelity.
"Our research has delineated 16 basic human needs, two of which are relevant to predicting fidelity versus cheating in romantic relationships: Romance, the desire for sex; and Honor, the desire for upright character.
What I call the Principle of Strong Needs says that the number of desired gratification objects increases in proportion to the strength of the person's need. An individual with a hearty appetite, for example, typically eats many kinds of food, whereas an individual with a weak appetite tends to eat a limited diet. A curious person wants to acquire knowledge about a variety of subjects, whereas a practical person focuses on learning mostly about topics that are relevant to their lives. A gregarious person is sociable toward everybody, whereas a private person has only a few close friends.
By applying the Principle of Strong Needs to the RMP motive of Romance, we can predict that people with a strong sex drive will seek many partners. Those with a weak sex drive, on the other hand, may be satisfied with only one partner. This prediction will not hold every time; there are numerous people with a high sex drive who are loyal to their spouse. Nevertheless, I maintain the Principle of Strong Needs can predict infidelity with a fair degree of accuracy.
When predicting the likelihood that a married person will cheat on their spouse, we should consider the strength of the individual's need for Honor in addition to the individual's need for Romance. People with a strong need for Honor place great value on personal character, moral codes, and ethical principles. They are loyal, keep promises, and take marriage vows seriously including the commitment to be faithful. Thus, a married person with both strong Romance and strong Honor is likely to seek gratification of their sexual desires within the marital bedroom. In contrast, people with a weak need for Honor tend to act out of self-interest. These opportunistic individuals believe there is nothing wrong with breaking a promise when it is to their advantage to do so. Consequently, a married person with a strong need for Romance but a weak need for Honor may seek sex from partners in addition to their spouse.
In summary, here is how my theory of human needs predicts the likelihood a married person will cheat on their spouse.
Strong Romance + Weak Honor = high likelihood
Weak Romance + Strong Honor = low likelihood
What happens if both needs are strong or both are weak? In such cases, we must consider the relativestrength of the two needs. For example, if a married person has strong needs for both Romance and Honor, but the need for Romance is greater than the need for Honor, we would predict an above average likelihood of infidelity. On the other hand, if a spouse has strong needs for both Romance and Honor, but the need for Romance is lower than the need for Honor, we would predict a below average likelihood of cheating."