I think people make way too much of infidelity, I am sure in the era of social media posts, it can be esp. humiliating and painful, embarrassing, but by that same logic, unless you are really naive, it shouldn't be hard to discover someone is unfaithful. I'd say 85% or more of the stories I've heard, people missed very obvious signs or ignored them, probably due to subconcious cognitive biases. It was always easy signs, not coming home, not answering phone, rumors, posts on Facebook or Instagram, it was never like a diabolical plot no one could see coming.
Last point, if someone cheats on you, end the relationship, reevaluate, and move on. Enough of the crying and years of anguish. It's logical that many people won't be 100% faithful. Doesn't mean don't trust people. just don't get so strung out on your significant faithful being your one and only, and look at them as a real, flawed person, with the capacity to make mistakes.