Ryder is my favourite GTA character. He may like to give CJ a hard time, but he is still his friend after all. I think he was the closest friend to CJ. At that time, Sweet didn't like him returning and kept yelling on him, while Smoke likes to bullsh*t him each time CJ asks about Tenpenny. Plus we never saw CJ joking with Sweet, or Big Smoke, but he does with Ryder in the mission " Robbing Uncle sam" I believe Rockstar had other plans for Ryder .
-1 Ryder was meant to die in the mission " the green sabre" there are quotes from the mission " hosue party" that would perfectly fit in that mission like : I will go round up some homies!" That will make sense, Sweet goes to the Mulholland Intersection and gets shot, Ryder goes to Big Smoke house and ballas wait him there and kill him or he gets shot with Sweet and dies, while CJ goes to check César. This would explain why Sweet and CJ never talked about Ryder anymore.
-2 Ryder was meant to be with CJ while he goes to SF! makes sense as well. Since most of the story in SF is about yay, Ryder would fit there exactly. He may have connections with drug dealers or something, that would help CJ and César bring down the Loco Syndicate.
Ryder doesn't hate CJ, there are a lot of examples where friends like to make fun of each other. If you watched the movie " Boyz n da hood" DoughBoy likes to mock Tre and Rick, but he still hugs them and roll with them. When Ricky died, it was the only scene that shows Dough crying, In the movie " Menace 2 Society', O-DOG always makes fun of Caine, he calls him a lil bitch and all. But he still his best friend, and almost cried when he died.