I'll never forgive myself for something
How did you feel about what you did that time?
I was a terrible person in that moment.
It is good to feel regret if you know that you have done something wrong, but you can't hold onto that feeling forever.  If you can, find a way to fix whatever damage you have caused, or at least apologize to anyone you have hurt.  Then, you can forgive yourself with time.
I don't want to. I will have everything to be the way it was. I won't forget
While regret is something good to feel as it shows you're growing, wallowing in it is counterproductive. Don't you want to move on from this and have a happier life? Why not finally move on, and just take this as a learning experience?