Is it permissible to delay the expiation for a violated oath of prohibition for years, based on the oath-taker or his uncle not paying for dinner, even though a third party has already paid for it?

You must get rid of the whisperings (waswas) and strive against them, and turn away from them. If by your oath you intended to prevent the man from paying, and you were the one who would pay the money, then you have broken your oath and are required to offer expiation for it. However, if you only intended to prevent the man from paying, then you have not broken your oath. Expiation is immediately obligatory according to many scholars, and delaying it is a sin. This opinion is more cautious and absolves one's responsibility, so one should hasten to offer it.