Sort of hard to do when the paparazzi's on your ass 24/7.
I don't think you are following.
Someone falls out of love. Or one spouse degrades or talks mean. Or someone has a job where they travel too much or takes too much of their time and energy. Or they ignore their spouse. Or they have different goals. Or one likes to stay in the other likes to go out.......couples drift apart.
THEN the cheating starts after those things when they don't get the attention or love. Cheating is not the cause it's a symptom of another problem earlier.