Many authors in this area ground their work in Systems Theory, Family Systems, sex research, personality theory and Social Psychology.They also adopt theories and research generated by sociologists, anthropologists and evolutionary psychologists.Also sometimes called "Retro Futuristic." Think of mobile phones as a simple example — once it was considered that they would only ever be available to the rich, and they'd never get any smaller than a brick.
With the introduction of the Internet, the definitions of affairs or infidelity become more elusive and complex.
Barash & Lipton poignantly wrote in their book Clinton's assertion that he did not have sex with Monica raised the question of not only what sex is but also how marital affairs are defined and whether sex or intercourse are the defining factors in infidelity.
These couples do not face a crisis when the infidelity is exposed.
Another example is a man who discovers his homosexuality in the later part of his marriage and comes to an agreement with his wife that they will stay married but both will pursue extramarital sexual relationships.
While extramarital affairs are very common, couples psychotherapists are often uninformed about how to address the infidelity crisis.