I believe people owe each other courtesy if they have to maintain decency in the future communications if they must be in each other lives for years to come. The only reason for having to stay in each other lives and be decent would be having minor children and having to co parent for years to come. There are no other reasons. You don’t owe him anything. It hasn’t even been three years. Less than three years of knowing a guy and not having any future entanglements does not qualify for owing anything.

As about him not being himself, if you didn’t catch him it would go on and likely would result in full blown affair. It’s not like he confessed that he made a mistake. He was caught in the early stages romantic affair with a coworker. So he has no leg to stand on