I agree with you, but, brain chemistry is weird, and "wouldn't cheat on them" is easier said than done and requires a lot of discipline in the heat of the moment when the situation arises and your own hind-brain and hormones are fighting you. A blasé attitude won't prepare you foe the sucker-punch.
I've seen grown people with multi-decade relationships throw it away because they got a tiny bit of extra-marital romantic attention, and the thrill regressed them to teenagers. In the majority if cases the cheaters' amors weren't interested in a long-term relationships.
I don't even care that much about what Jensen did, I don't even know what his marriage is like. It wouldn't bother me if he stayed on Nvidia. But people are defending him in a way that comes off less like "we can all make a dumb mistake on the wrong day" and more like "all men want secretly to ditch their wives, and his mistake was doing it with a spy."