There are few things that hurt more than the first boy with which you ever fall in love.
Buffy stares at Xander across the room. A lot more shit has happened to her and around her since Angel staked Darla in the Bronze, and god knows more will, constantly, endlessly. Someone is killing potential Slayers. Someone who's maddeningly good at it.
Dying hurts. You'd think it wouldn't, since it's supposed to be the most profound part of your life - you're breathing, then you're not. Your existence is extinguished.
Buffy stares at Xander. Xander, of all people - Xander asked her to homecoming. Xander, through all the shit, has never wavered in himself. Throughout such massive changes, Xander growing up has gone past their radar. Xander was the core.
Living hurt, too, but in different ways. Dying hurt in that all your nerve endings sizzled and you wanted to scream and scream. Living hurt in that you couldn't say anything at all.
Buffy stares at Xander. Xander, who hated vampires, point blank. Who always wanted the best for her, and more importantly, of her. Xander, whom she loved unequivocably, couldn't live without. Xander, who'd been there from the beginning, who'd seen Jesse's death. Xander, who never told her about Angel's soul.
It took her a long time to realize it; there's always something more important happening, but not right now. Buffy doesn't move, doesn't hold her stomach, doesn't cry, doesn't scream. This is the kind of living hurt. "He knew Angel had his soul."
Buffy walks away from Willow. It feels like she's swallowed tacks and now they're rattling around in her gullet somewhere, tearing little bite sized holes in her stomach. It's okay.