I wouldn't either. I'm as confident about that as I could be about anything.
Excet that I have.
It was many years ago in another lifetime really (I was in my 20s) when I was a different person. I was in a very unhappy relationship and, at the time, I couldn't see a way out of it for various reasons. Like many people who cheat, I wasn't looking for a way out, I was presented with an opportunity that made it easier to stay. He was single.
It only lasted a few weeks before I ended it and realised that I didn't like how it made me feel about myself or what it said about me as a person.
And that is how I know I'd never do it again.
I'm older now and wiser and know that it doesn't solve anything and I've left any subsequent relationship I didn't want to be in.
So would any man cheat given the opportunity?
Some would. Some wouldn't. The problem for most people is that they don't ever know for sure that they are with one of those who would or not. And, even those who wouldn't, might if the circumstances were right.
I don't think that that means all men would because I've certainly chatted with men (when single) who've made it quite clear to me they were married and loyal. That doesn't mean they'd never have their head turned by someone but they definitely weren't just up for it if a (perceived) opportunity arose.
I do think women who believe they are in happily sexless relationships are being naive though.
I've read a few threads on here where a woman is devastated to discover her husband's affair only to reveal that they haven't had sex in several years.