Why do RW and Melvin befriend TJ? How does this friendship illustrate one or more of the central ideas in the novel?

TJ tells Stacey that his friendship does not matter because he has better friends now who treat him like a man and who are white. Of course he means R.W. and Melvin Simms. They are just using TJ so they can make fun of him and set him up for a crime that they have planned. TJ is easily manipulated and exploited by these two boys.