I'm still not sure why Kujo ended his friendship with Aoki. Did it have something to do with Aoki following him around too much because they sort of split up after Aoki went insane on those lower-grade students and Kujo told him to stop following him around. Also, at the end Kujo remembers Aoki saying to him, "Take me with you." Anyone who's got it down is welcome to reply.
I took it that Aoki was the one who remembered the "Kujo, take me with you" line, but I could be wrong.
I think Kujo was ignoring Aoki for a mixture of two reasons. The first one being that, like you said he sort of depended on Kujo too much. Also, when Aoki is beating the other student with the baseball bat, you can see the expression on Kujo's face, right before he decides to walk away. The look on his face, was sort of a look of disgust toward Aoki, for what he was doing. I think Kujo just didn't care as much about beating up other kids, or he just didn't care about it at all. That's all Aoki wanted to do, really.
I died then I thought of you and came back to life. How can you think if you're dead?
Aoki went nuts becuase Kujo was begining to grow tired of his roll as leader saying things like "I'm not fit for this". And durring the scene when Aoki is dishing out a beating and asks for guidance from Kujo, Kujo simply tells him he should know how to handle the juniors Aoki kinda takes offense to this becuase Kujo is supposed to be his leader, and moreover friend. At that point Aoki is also tired of Kujo being the leader and takes matters into his own hands so to speak, and then you have the rest of the movie with its tragic end :(