Do you think it's strange that Cassie doesn't seem to have a BFF? Her closest ties are with her family (Stacey, Christopher-John and Little Man). She rarely does anything without one of them, and she doesn't form close ties with anyone at her school. Considering the risks we see with friendships outside the family (think Stacey and Jeremy or Stacey and T.J.), it's probably no accident. Roll of Thunder, Hear My Cry shows that friendship can be a dangerous thing if you're not 100% certain of the other person involved.
In the world of the novel, true friends can be determined by the sacrifices they are willing to make for you.
The relationship between T.J. and Stacey shows that some friendships are just not worth the risks.