You'll never forget the things you have done that you regret. Everyone makes mistakes, sometimes we do what we felt was good for us or right for us even at the expense of others. It sounds like you are feeling some guilt for some things you have done. Guilt can be a positive emmotiin. It keeps us in check with our conscious. Most people do something wrong and they feel bad about it. It is a normal feeling. Don't let your guilt consume you. Because you did something wrong doesn't make you a bad person. It just means you made a mistake and wanted things to go differently.

Try to come to terms with what ever it was you did. Was it accidental, on purpose or even malicous? What was the consequences of it? Did someone's feelings get hurt, did someone physically get hurt or die? The only thing you can do at this point is try to worm on yourself and not make the same decision. Going to the people that you have wronged and making ammends can be a way to release some of the guilt you are feeling. Don't be too hard on yourself.