To stay grounded, he needed constant arousal, constant physical stimuli, but every arousal brought with it the sensation of splitting, of tumult in his mind between ... he didn't even know what. Not just demon and soul, he could laugh at the stupid simplicity of that dichotomy. That was Angel's story, but Angel had always been a bit of a simpleton. Not like split personalities either, that silly telly movie Sybil, some bird with a whole cast of characters parotting inside her.
Not like that at all. Just ... a lot going on. A lot going on in one huge echoing hollow place, all at the same time. That place being his mind.
Buffy didn't understand what had come back to her wearing his face. He didn't understand it either. One minute he was himself, right down deep in the selfness, in the moment, Spike and no-one else. And then he was other, except that other—it wasn't the demon, not precisely, not merely, not only—was himself too.
He'd tried to tell her about it, to be honest and open. But she still didn't know.
It wasn't knowable
amazing look inside Spike's mind, especially like the lines I bolded, the thought of the reflecting and echoing, but hallow, not building, diminishing maybe, is a most haunting image