Have you ever had a bad experience and then replayed it in an endless loop in your mind afterward? Perhaps even for days after? Yup, I've done that at times, too.
It really doesn't help the situation at all to dwell on it like that, however. In fact, if there's anything in the situation that needs solving, forgiving, letting go or any other type of action, that's less likely to happen when we obsess over the experience repeatedly. Our minds are so full of the negatives that we can't even be creative when it comes to a solution. And if forgiveness is required, we won't come close to that if we continue dwelling on how horrible the experience was.
Try to shut down the "repeat" and "play" buttons in your mind. Do something constructive and challenging that will take all your focus. Throw yourself into some new project. Let yourself have a feeling of accomplishment when you complete something challenging. Spend time with people you love. Let your focus be on good relationships and friendships. Totally switch your focus.
Then you can return to the situation with a better ability to assess it and determine any action you need to take. You'll be far more creative and far more willing to let go and move on.