Everyone, including you, makes mistakes. To be human is to err, remember? This is when your ability to forgive steps in. You have to let it go because life is too short to hold grudges. The more malice you have for someone, you dig deeper into that negative abyss of yours and bitterness starts reflecting in your actions and words. He or she wronged you, call it out. Communicate or do anything to not let it dominate your life. It happened, you accept it, acknowledge it, but do not ponder over it so much.