He's not sure how to read the expression on Scott's face. He shouldn't be surprised with as long as he's been gone, but some part of him has always expected if he ever came face to face with his best friend again, he'd still be able to figure out what he was thinking, feeling. But the nuances are more subtle now. Scott's holding back in ways he never did, and Stiles knows that's his fault.
He draws in a breath and lets it out slowly at the word why. How could he not know? How could he not understand why? But then he continues, and Stiles is actually thrown off guard that he's realized what the ritual entails. A trade. Shit.
Stiles rubs a hand over his face, nose still sore from where Allison had punched him just a few days before. He looks away, off into the distance. "Because I wanted to give her back to you. To Lydia. To Chris." His voice is quiet. Honest. Because it wasn't supposed to be Allison who died at all.