I have this friend, what do I do?

I've been thinking a lot about a friend lately. His name is Dylan. We've known each other for 3 or 2.5 years, and he's always been the same. He hits me as a joke, suddenly gets angry and doesn't talk. Once we were walking on a dangerous street, and he got mad at me for no reason and left me walking alone. All I remember is that a man in his 50s was following me.

Whenever I approach another friend, he gets angry and walks away. It's always the same. He's very rude and has no respect. He and I walk together. Yesterday, he left me walking alone because I had to spend less than 5 minutes talking to a teacher about something he knew was important. He didn't wait for me, even though I told him to wait for me and that I always wait for him no matter what. I honestly don't know why I'm still his friend...

Any advice on what I should do?