I do think that everyone is capable of having an affair. That doesn’t mean everyone will and it also doesn’t mean that we shouldn’t trust our partners, but everyone is capable.
But there’s a difference between saying that, and essentially calling people who trust their partners stupid, deluded, naive, sneering at them in the way that the OP and others on this thread have done.
And tbh when people are that sneering and horrible it makes me wonder what their relationships were like and whether the situation in those relationships led to the affair in the first place.
Because while there are absolutely some people who will cheat purely for sex and because they can, affairs are rarely black and white, and there are almost always issues which lead to them happening, even if the affair isn’t justifiable.
But an affair essentially wipes out all wrongdoing on the other side. You could be as abusive you like to your partner, but as soon as he has an affair the end of the relationship is 100% on him.
And let’s be honest here, it’s not deemed acceptable to leave a relationship. How often do people come here saying their partner has left, and the same posters who are sneering at the trusting right now will tell the OP in no uncertain terms that there is an OW and not to be so stupid as to believe there isn’t.
So even if a man leaves because the relationship is unhappy, he’s already being painted as an adulterer even if he isn’t.