I dunno. Unfortunately, I know of very few relationships that haven't been touched by infidelity. Luckily, I know of more that survived it than not.
A couple we know well went through a bit of crisis when he was "addicted to Internet porn" but they came through it and are now missionaries.
I still believe that infidelity is not that rampant. Maybe I am living in a fool's paradise, but I think outside of a few enclaves, most people are trying to live decent lives.