I think the attitude towards Jackie changed when he asked for "head writer" status in a contract negotiation. Fred got downright hostile towards Jackie after that. Before that they were so close that they spent wedding anniversaries together (which lead to the Rainbow Room)
Maybe between Fred and Jackie, maybe.
But, I forget the details about this. It is a common thing to give a person a prestigious title in lieu of money. And, we all know about Howard and him parting with marbles. So, did Howard offer him this title or did Jackie ask when the money was coming through?
Fred can be a little petty prick. He never forgave SJ for networking a record deal for his band and King Norris stayed in the sewers. Everyone visited SJ in California for years after he left, but Fred couldn't let it go.
But, Howard, all signs point to Jackie wanting more money than KROCK, I mean Howard, wanted to give being the cause.