WIY,
To forgive someone (who does not ask for forgiveness), you must be able to forget. To forget, you usually need a change of your situation (where you live, go to school, friends, etc). Another very helpful strategy is to talk to someone you trust (sibling, spouse, your child) about the situation you were in and discuss the facts of what happened, the people involved and their personalities. This should allow you to acknowledge/ accept what happened and move on.