I'm so sad, I don't feel like I have a best friend anymore.
Oh no, why don't you feel like you have a best friend anymore?
I said something really hurtful to him and he's not speaking to me.
Sometimes we say things we don't really mean when we're angry. Talk to your friend and work out your differences.
I don't know, I've tried to call and text him but he won't respond to me.
I know you feel very bad about what happened, but your friend is hurt and he needs some time. When he's ready, talk to him and apologize for what you said. I'm sure you can save your friendship.