Some states adultery is a crime. It ranges from a misdemeanor with a fine to jail time. It is up to the state to pursue or not pursue/prove that adultery should be prosecuted. But in trump's case, it is not part of the indictment.
But morally, it is a crime against the vows to the woman that you are married to.
I would figure that after all the self research that people put into their cures on covid, constitution law and the truth of vaccinations, that you would also do a simple search of is adultery a crime.