"Heaven," she had sung. "I think I was in heaven." This is what Giles remembers most from this ordeal. His own songs - the words are already fading. The same is true of the songs sung with the others, songs sung by others. Her words stick in his mind, and, really, why shouldn't they? It's his job to pay attention to her, or at least it used to be. Every syllable, every inflection, every emotion - that was, after all how the damn thing worked: everyone doing the group sing knew what their partners were feeling, and those feelings were the basis for their melodies - everything of hers were in his memory as if they were his own.
He remembers her feelings. And she remembers his.
The harmonizing across distances that happened right before they encountered Sweet - it was a complex thing. He knows from his books that the distilled empathy worked strongest between those who were already strongly bonded: couples, blood family, and, yeah, Watchers and their slayers. The others couldn't know his thoughts. Dawn might know Buffy's, but nobody but Buffy could know his. He hadn't sung them all.
So it's two hours later in the Magic Box, and here's Buffy standing in the entrance with that look on her face. Indignation, confusion, pain; he's only seen that look once before, and that time she didn't have the strength to break him in two. He absently wonders where Spike went.
He puts down the book he was about to reshelve. "Buffy," he says as warmly as he can when he knows what she knows. She takes a step inside, and her arms are crossed over her chest.
"You really can stay," she says; he cringes as he realizes that she had heard him, even if she hadn't understood until now. "I like you here."
The spell has worn off, but he doesn't need to know her thoughts to know what she's thinking. He flashes a smile and says, "But that's not all you wanted to say, is it?"
She mirrors his watery smile and says, "No." He guides her to a seat, schools his features, waits. It's nearly three minutes before she speaks again.
"In The Bronze," she begins. "I - you thought - I mean, when I was doing the big burn-up-and-die Lindy." She tries to meet his eyes, and he looks at the tabletop. "God, Giles, I can't even ask."
"Then don't," he states quietly. "Know that I'm glad Spike stepped in, whatever my thoughts were at that moment."
She hugs him. "Thanks," she says, and leaves with that - not angry or sad or anything, just content with his answer. He knows she knows he only wanted what would bring her happiness. It would've killed him if Spike hadn't done what he himself couldn't, and he knows she knows that as well. And he knows, even if he does end up leaving her, she'll never break his trust.
No one need know that he'd hoped she'd burn back to peace.