When the book starts out Milkman and Guitar have a relationship where Guitar is the older more knowing friend and Milkman is the younger friend who listens and follows Guitar around. There relationship does kind of change throughout the book. As the story goes on, Milkman kind of fears Guitar and stands up to him in conversations. This change in relationship also follows with a distance between them.
At the beginning Milkman and Guitar go over to the Pilate's house together. In the book it says, "Guitar, being older and already in high school, had none of the reluctance that his young buddy still struggled with, and was the first one to speak." (pg. 36) This shows how Guitar holds the more mature role where he introduces himself to Pilate first and then Milkman follows with guidance from Guitar. It seems kind of like a sibling relationship back then. They get along pretty well and it seems like Milkman set Guitar as an example for how he lives and acts.
When Milkman gets older it seems like he finally stands up to Guitar and is scared of him killing him after he finds out Guitar is part of the Seven Days. In the story it says, "Milkman drank his up quickly and ordered another before asking Guitar, "How come they call me Milkman?" "How the freak would I know? That's your name ain't it?" "My name is Macon Dead." "You drag me all the way over here to tell me your name?" "I need to know it."" (pg. 84) This quote shows Macon demanding something from Guitar for the first time and being the leader. We then see more scenes where Guitar tries to lecture Milkman and he comes back to fight what Guitar has just said. Then we hear the Seven Days joining of Guitar. In the story it says, "Guitar, none of that stuff is going to change how I live or how any other Negro lives. What you're doing is crazy. And something else: it's a habitat. if you do it enough, you can do it to anybody. You know what I mean? A torpedo is a torpedo, I don't care what his reasons. You can off anybody you don't like. You can off me." (pg. 160-161) This quote shows how Milkman senses that since Guitar is in the Seven Days that he could kill him and he is afraid of that happening. He is concerned for his friend and is now trying to look out for him by telling him the reasons he shouldn't be apart of this organization.
All in all, the book shows Milkman and Guitar's relationship change. They start off close and sibling like then they go into a time of distance and fighting and even fear of the other by Milkman. Their relationship is quite interesting to watch throughout the book. At first we don't expect this great of a change between them but by then end we see how it is necessary to have this change between Guitar and Milkman's friendship.
*quotes from the book but somewhat censored and have only read thru chapter 9 so far.