The motivating factor in many cases of infidelity is lust or sexual desire. What psychologists William Cupach and Brian Spitzberg describe as having "the wish to experience sexual union with another." The factors that motivate this are far from obvious. Psychological research overwhelmingly shows that lust is an expression and projection of emotional memory. It is as much linked to past events as the present realities of another person: "Yet whatever is triggered in your psyche regarding the lustful qualities of another person is something specific to your own history." The unique experiences a person has in childhood, for example, can later affect how they experience sexual desire. The base components of lust are therefore linked to these deeper historical events. When a man lusts after a woman, he is projecting a "fantasy" of his own making, based on these components.
If we assume that cheating must be driven in part by a sexual desire, it is crucial to understand what that desire actually is. Research shows that lust is so powerful because it is a reflection of the self. Lust occurs when a person projects their unconscious memories of attachment and love, as well as their present ambitions, interests and passions. These two factors work together to create a fantasy version of a potential affair partner in a person's mind. As psychologist Dr Mary Lamia writes, "...at times lust is an unbridled sexual attraction that seeks expression, where the physical appearance and attributes of one person ignite emotions of intense interest and excitement in another. This is because such passion is a construct of implicit memory that becomes enhanced by conscious imagination."
There are several issues with this claim. Falling in love with a fantasy may hold true for long-term infidelity, where feelings have been allowed to grow. Yet, this does not explain instances of "unplanned infidelity", where the cheating party has not met the person beforehand. Research shows that these idealised projections have a lifespan. While lust can obscure the realities of a person, it cannot do so forever. In affairs, where unions can last years, lust does not explain how these develop and sustain.
[P1] Infidelity is predicated on lust [P2] Lust occurs when a person projects a fantasy onto another [P3]Affairs are predicated on fantasy
Rejecting the premises
[Rejecting P1] Infidelity is not predicated on lust