Humans are naturally inclined toward novelty; the "bright and shiny new toy," if you will. And Kreizman says boredom and isolation can make almost any other pasture appear greener.
Which is why it's so important (ESPECIALLY in long-term relationships) for everyone to make a conscious effort to keep things interesting. It's a requirement for ensuring healthy, satisfying bonds.
Cheating is resplendent in justifications
It's no news that the act of cheating is ultimately done for selfish reasons -- to be happier, feel more attractive, chase a few thrills, be admired, or more simply to get their rocks off. In the process, we become really good at justifying our wrongdoings so we don't feel guilty.
"What happens when people deviate from their values is they start to rationalize their decision," Dr. Lombardo says. "They develop beliefs that it's OK to do, or they deserve it, because the cognitive dissonance is too tough. Cognitive dissonance refers to acting in one way despite believing something else. And this can be extremely stressful. In an (unconscious) attempt to reduce this stress, people justify their actions. As a result, they may be more likely to continue an affair because of this cognitive attempt at protecting themselves."