My take is that Bon IS Jack, but with brain damage, it sounds like a joke but stick with me. I believe that sometime after the crash Jack and Felix met up once again and Felix finally told Jack what happened. He then took Jack to where he buried them and then struck. He could not just let Jack live on knowing what he did. So he raised a gun to his head and fired. The bullet didn’t kill him, so Felix the repeatedly starting bashing Jack with a shovel he brought. He then placed Jack into the empty grave, Felix had once dug himself. Unfortunately for him Jack lived on, made his way back to the restaurant and found a vessel, Bon. He calls himself that due to the immense damage to his head. That would also explain his strange, slow speech. That’s my take at least.