Done. He was just done.
Years of thinking he was making a difference. Wakeful nights made worse by the company of the bargains he's made, protecting this sad little ball of dirt. Lives he's taken and lives he's given: his own and others. He's survived one alien invasion too many. He's outlived too many lovers. He's made the dreadful choice--the worst choice anyone could ever have to make--and become the monster Ianto, with Jack's revolver to his head, once named him.
Alice's eyes eviscerate his heart, leaving Jack flayed and bleeding in the only way that still matters.