The Rum
When Jack Sparrow was young Jack Smith, he hated rum. He hated what it did to his father, after his mother had left. He hated the smell and he hated the small sips he had tasted. Rum was the root of all the evils in young Jack Smith's life. His father's violence, the lack of money. Rum was vile.
When Jack Smith was a young man, he learned to appreciate rum. Just the odd glass, now and then. However, it was his drinking partner he preferred to appreciate. Bill Turner had taken Jack under his wing and Bill was a pirate. Now Jack was a pirate too, no longer Jack Smith, but Jack Sparrow. And unless he wanted to be the butt of everyone's jokes, rum was something he had to drink.
When Jack Sparrow was a bit older, he was Captain Jack Sparrow and Bill Turner had become William to him and Bootstrap to everyone else. And rum was something to be savoured, because they rarely got some really good rum, and when they did Bill would teach Jack new ways to enjoy it. Rum was their drink, and Jack Sparrow was in love, but no one could know. Not when the slightest hint of weakness meant mutiny.
When Jack was even older, he sat on an island in the middle of nowhere and drank all the rum he could lay his hand's on because HIS ship was gone and William had just stood there. William with a wife and kid, living out there somewhere. A son with his father's name. And he barely tasted the rum as it poured down his throat; it was only to hide the feelings of pain and betrayal.
When Jack Sparrow had been on his own for a year, it had been eleven months since he had last touched a drop of rum. Rum was their drink and William had betrayed him. But then he heard of William's expulsion from the ship. He'd stood up for him. And that night he bought as much rum as he could carry and spent the night drinking it away, for him. After all, rum and the memories were all he had left now and the two had become so intertwined that he could no longer have one without the other. And maybe if he drank enough, it would fill the empty hole inside his chest, that he didn't remember having before.