He watched her as it hit her. He knew it wouldn't be easy. Hell, it was hard enough to have to tell her. To hear it, and not already know it? He couldn't even imagine it, really. He didn't say anything as she tried to calm herself down. She didn't need him blathering on while she was trying to process it.
And there it was. That pointed question he really didn't want to answer. And there really was no backing out of it. Not now. "Willow...she tried to bring you back, but...it didn't work because it was a human death, natural in the sense that it wasn't a supernatural force." This was where it got messy. But again, Spike had no plans, and decided to basically be blunt with her here as well. Like ripping off a bandaid, right? "That little magic addiction? Yeah, it didn't get better. She went on a tear. Wanted revenge."