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.
I guess it all depends on what you mean by "that rampant". I don't think everybody is doing it, but I certainly wouldn't be surprised by a figures that hovered around half of all marriages or slightly better.