Jesus Dude, that is NOT a hypothetical. I am 47 and I did not get married until I was 36. You don't think in 36 years I had a layup opportunity for punani with a hotty where there was an absurdly high likelihood that I would not get caught? That's happened to me bro. That's happened to a lot us us.
And 100% of the time I had made a commitment to someone I walked away. Not Going. There were times where I regretted that I was in a committed relationship. There were even times when something like that happened, and the fact that I could not engage made me rethink and then reshape the boundaries in my relationship.
Maybe we are just wired different. But to me it's easy. My word means a lot to me. Obviously more than yours does to you. In my mind, If you can't keep a commitment that you made with a conscious choice, to a promise you crafted yourself, that you can rescind or alter at any time with a simple conversation, then there is literally nothing your word is good for.