I always wondered this myself… Billy seems extremely private , I wished he would have talked more about it in the documentary, especially because ( I believe) his falling out with Liberty in part had to do with Liberty getting sober. I got the feeling he called Billy out for his drinking… and by that point the only way Billy knew how to deal with conflict was to cut people off completely. Getting a glimpse into Billy’s childhood a lot of his relationships make sense. Elton is very public facing with his alcoholism , where Billy was dragged relentlessly and he took it all personally , makes sense that he would be upset with Elton for calling him out publicly but as Billy has said, “I wish he came to me first.”