Cheating is not. It's certainly a valid reason to end a relationship but you do not have a right to another person's affection. If they behave like a jerk, walk away.

The sorts of mentalities that see cheating as a crime, do that because they see women as self-stealing property or disobedient chattels. They are in other words disgustingly abusive, controlling and sexist. In this case it is the anger against the cheating, not the cheating itself, that is the violence.

Exactly. Furthermore, the law does not delineate what is right and what is wrong; that is a moral issue. It is a "best effort." The absence of legal ramifications does not mean that something is morally acceptable.

Many people agree that revenge porn is wrong, which is why the law (as the lowest common denominator) now reflects that sentiment.

No, because it is harmful. It harms a person's reputation. It also violates a person's privacy.

But cheating on someone shouldn't be criminalized even though it hurts at least as much

This is a false choice.

Society has decided that punishing people for cheating is a stupid idea. Society has also decided that punishing people for tax fraud is a good idea. These things are both completely irrelevant to any laws on revenge porn.

So by that logic, cheating should be illegal too.

By the way, society hasn't decided anything because it's not a sentient being.

The politicians running our governments have decided that punishing people for "tax fraud" is a great idea, mostly because they don't want people to stop paying taxes.. which everyone would do right away if there was no punishment for disobedience.