It hurts, thinking about her. It hurts him down to his soul (and he suspects that if he were to lose his soul again it would hurt still. She was just too deep within him) to remember her voice and her smile and her heart. It hurts to imagine what they could have been, if they'd just been braver, smarter, luckier.
And it hurts to think about what they were. Even before the idea of "more" ever crossed his mind. He had loved her so much and in so many ways. Friend, sister, lover, partner. Lifetimes worth of love in only a few short years (He understands Spike's love for Buffy in ways he will never be able to explain).
And no one understands. We is gone and Gunn is gone and Fred is gone (and the memories of all of them, of all that loss and all that love, of yet another one of his families gone. That hurts more than he thinks about, past his soul and deep down into his bones, into his ash) and there is no one left that knows.
He has seen the books. Mentions of Darla as his sire and Drusilla as his victim (but never enough about the complicated life he shared with them both) appear on the pages of nearly every book he finds himself in, and of course there are paragraphs, pages, entire sections devoted to his relationship with Buffy. About the vampire with a soul who loved a slayer and the slayer who loved him back (there is no mention of the second vampire. The one who loves the slayer now, and is loved by the slayer now, and he has to wonder how long it will be before the books are rewritten).
But there is never anything about Cordelia. And no one left who understands.