>“I tried to find it, of course. The spark. The missing… the piece that fit.”<
The spark in question is his soul but i think it sums up his whole life ,always looking for something to make him feel alive. It can be hunting slayers that no one would face just for the thrill or his twisted addiction to pain and violence. It can be his desperate need to be loved , to feel accepted. His speech in seeing red just shows how seriously damaged and fucked up he is , like he is constantly burning inside and he “just wants it to stop” .Ironic that he found peace by literally burning for the world he wanted to save when he was a cruel soulless vampire.