It would be hard to quantify for statistics, but I think it is really common. How many men carry on full out affairs is probably lower than one night, or a night at a bachelor party. From reading that book, the stress alone, the paranoia, shyt sounded a few degrees removed from the paranoia of drugs and crime. Multiple phones, multiple names, stash houses, cover stories, high stress tests all the time.
I know every kind of cheater, most I would say are situational, with a pattern, like a crime of opportunity, once a month, or whatever.
I know people with houses in different states, I know guys with a different Iphone for business travel, I know guys that it's just commonly accepted they stay out a few nights a week or a month.
The least common is the full on affair, with another person, where is regular and scheduled, and a separate relationship entirely.