The only way to know for sure is if he never does it again. Other than that, you either believe him when he says he’s sorry or you don’t. Some men are truly sorry and some are very good actors. Some are sorry they cheated and others are only sorry that they got caught. There’s no way to know for sure in the short run if his regret is legitimate. What do your eyes, ears, heart and gut tell you?
Thanks for the question.