It isn't practically possible to forget a significant event that happened in the past. You can try to rationalize the situation, try to accept it and then try to outgrow this feeling.
Have you been able to share about it with anyone?
its quite difficult to forget something, when you keep saying you gotta forget it. just let the memory flow and dont bother yourself with the past , even if you seem to remember. i know its difficult, but its worth a try