I have no idea what oath or commitments he made with his wife

And I don’t look to CEOs for moral guidance and leadership. Ever.

I might evaluate someone’s good sense before investing, and this was bad decision-making, but it’s hardly the whole of his career.

Don't confuse your own religious views with those of everyone else. Probably your first mistake.

Good point. Most people do make oaths to our partners. "Till death do we part."

But then we culturally decided divorce doesn't count. "Till death do we part" became "Till death or major or minor inconvenience do we part."

Or we just culturally decided that a centuries-old tradition didn’t mean we had to forever put up with something we only later found out we’re unhappy with. Marriage should not be a life sentence nor an unbreakable commitment.

Funny things, the rules we make up to justify nonsensical behaviour.

Only some religious traditions actually involve that oath. Jews have practiced a religious version of no-fault divorce for thousands of years.

People also promise to love and honor each other (until death...), and see how well that's working out for many. Cheating is often only the consequence of that failure, and as someone "outside" - who are we to judge the people who are inside of the relationship?

Have you considered the possibility that sometimes people give their spouse permission to have an affair?

Have you also considered the fact that you can get married without taking such an oath? A wedding ceremony is not how you get married. You get married by signing a document that says you are marrying the other person who signs the document, and then filing the document with the government. Marriage is a legal arrangement that primarily covers property rights and certain legal decisions (e.g. the presumption that your spouse can make decisions on your behalf if you are incapacitated). Even in the few remaining places where cheating has any meaningful legal significance divorce lawyers often advise clients not to bother -- it is rarely worth pursuing and most people just want to finish the divorce as quickly as possible and all filing for fault will do is raise your legal fees (for little tangible benefit).

No…

I don't remember any oath about not sleeping with another woman, in my language and culture. Maybe there is one in his language in culture, but I am not sure about that. There is one about being together in good and bad times, but "cheating" does not imply separation or divorce, just having some time with someone else. It is even something agreed in a marriage in certain circumstances of health or age.