I haven't really made a mistake as you have but sometimes I do think back to the minor mistakes I have made and it gets me upset to know we can't do anything to change the outcome, but don't use this to fuel anger, use it to fuel self-improvement. It takes time to get over things and even then you don't really get over things, but everytime you feel the pain and regret, take it as a reminder that you should watch what you say and do to others. Once you turn a negative thing into a positive thing that assists you in life, it's easier to bear with it because at the end of it your brain understands due to your mistake you have improved. But don't improve yourself only in one area of life, reassess everything and make sure nothing like this ever happens in all areas of your life.