What is the ruling on swearing by divorce, saying: "I swear by Allah, if night falls upon you outside again, you will be divorced," and how can I repent from it, knowing that the wife has not been late at night after this oath?

Your oath has been made. Divorce does not occur except by your intention. If you intended to pronounce divorce yourself upon her delay, and did not intend its occurrence merely by the delay, then it does not occur except by your pronouncement of it. Your breaking of the oath would be by not pronouncing it, and you would be liable for an expiation for breaking an oath. It is better to expiate for your oath and keep her, based on the saying of the Prophet, peace and blessings be upon him: "Whoever swears an oath and then sees something better than it, let him do what is better and expiate for his oath." However, if you intended the divorce to occur merely by her delay, then this is a conditional divorce, which, according to the majority of scholars, occurs upon the occurrence of the condition it was tied to.