why do supposed Stacey thought of T.J Avery as his best friend?

I think that they were actually friends. There was a kinship of sorts although the friendship was far from perfect. Stacey is a sensitive introverted sort of boy and T.J is charismatic and extroverted. In many ways they are character foils to each other. Stacey likes T.J's energy while T.J is attracted to Stacy's stability. T.J. certainly manipulates Stacy which makes their friendship incredibly flawed. Still, I think they do care for one another.

Stacey was/is the only one who gives him the "attention" he needs