If that were the case, there would hardly be any cheaters. And women demonstrably do it more often than men, they usually just do it more intelligently.
In real life, you don't necessarily need bad friends or enemies to lead you down the wrong path. Some people cannot be faithful by nature, others become victims of circumstances, sometimes. All it takes is a single insult in the past life, an unfulfilled longing that still simmers, and finally the right trigger, for example, a life crisis, neglect, midlife crisis, or something similar. Everyone has something like that inside them. Whether or not one gives in when the worst comes to the worst depends on each individual. We are not all equally strong.
Each of us has special strengths, but also at least one Achilles heel. And if the sore spot and the trigger are located at this point, fate can strike very easily. And when that happens, a dam can break, as a result of which even you and I can become cheaters.