I want to tell my childhood friend, who loved me, that "I'm sorry I hurt you"
Do you want to know how to avoid hurting others in the future?
Sure, do you have any advice for me?
Whatever you have done in the past to hurt your friend, it is always good to take responsibility and apologize for it.  They will come to forgive you with time, as long as they know that you are sorry.
I feel bad for my friends who got hurt because of me, I know exactly how it feels to be on their shoes.
Not only that, but I'm sure your friends will make it easy for you. Friends are great like that. You sound like a good person who has matured a lot since you were a kid.