I like JD a lot, he and Shep are the two guys on this show that I'd actually like to have as friends, but I think his friendship with T-Rav is a little pathetic. Have you ever noticed that JD always seems more happy and excited to see Thomas ("T-Rav-A-Nation!!!", "T-Rav is in the house, y'all!!!") than Thomas does to see him?
Thomas and JD have know each other for many years, but I think that for most of that time, Thomas probably didn't consider JD a close friend, just an acquaintance and occasional drinking buddy. I get the same vibe from JD that I do from Craig: a solid upper-middle-class background, in no way under-privileged, but without the old Southern lineage or inherited wealth that would place him in the top drawer. He seems quite successful, but he's probably had to work hard for everything he has and that's not something that a snob like Thomas would respect.
Then T-Rav crashed and burned and went to prison. When he got out, a large section of upper-crust Charleston gave him the cold shoulder and suddenly he was alone. JD was there to take the place of the old friends Thomas had lost. And for JD, it was like being the nerd who finally gets invited to eat lunch with the cool kids in the cafeteria. And being on the show as T-Rav's best friend (and godfather at that ridiculous "second christening") makes it official.