Carrying a grudge around for someone or something is such a burden. It requires precious energy to keep hating someone for something they did a long time ago. It’s a gift to yourself and to them to just let it go and move on. You can do this by recognizing that the person who wronged you is a human who makes mistakes, by recognizing that they were young and immature, recognizing that they have different values, or a host of other reasons which might explain their behaviour as less of a personal attack to you. You will be much happier to simply let bygones be bygones and move that grudge out of your heart.