According to RAS they all three were childhood friends though I think Betty and Jughead were more friends via Archie. I'm not sure there was more to the JA falling out other then Archie ditching him and their trip for Grundy and then never talking to him or apologizing about it. It seems like Archie ditched him then ignored him which is pretty crappy but he was in his own little Grundy sexing world. I don't know if Jughead is also estranged from Betty or if he's just isolated himself from her just like he has everyone else. But we go from him totally withdrawn in the pilot to starting to reconnect to others first through Archie and then through Betty. Now that he's part of the social circle, I'm wondering if Reggie and the others will ease up on the bullying.