What happened to cause that? Whatever it was, I'm sure it was a misunderstanding, no need to worry about it. Best friends do not come and go that easily, and I'm sure things will be okay.
About the breakup, don't be upset about it. It just proves that he wasn't good enough, and you definitely deserve better. There are jerks out there, and they are not worth being upset about. You just have to remember that your friends will always be there for you (Including the one who slapped you, I insist on the fact that it was a misunderstanding), and things will get better.
And sorry for the late reply, I was at my piano lesson, and as the server was down before I left, I couldn't inform you.