Disclaimer/author's notes: Naruto is owned by Masashi Kishimoto, not me, no profit involved. No warnings, set after the Valley of the End. Uchiha and angst should be synonymous though.
For a moment—and only just that: one moment—Sasuke considers turning back, but then he listens and hears Naruto's breaths dying. With every breath that Naruto takes, Sasuke almost forgets his purpose so he listens to Naruto no more and leaves Naruto like his rapidly-fading life means nothing (Sasuke tries not to feel sad. It's the idiot's fault for being stupid and thinking bonds mean shit).
Besides, the only one that Sasuke will watch die is Itachi; everyone else can just stay out of his way or burn as Sasuke sets the path he travels on into black flame. Sasuke doesn't want to do this, though; he isn't Itachi and he doesn't want to kill because he can. But he has a purpose that he must fulfill. He owes it to his family (even if Mother wouldn't want this—Sasuke's hatred, brother killing brother—Sasuke ignores that. Mother is dead. Itachi is alive).
Still, Sasuke stops for a moment and thinks about the person (friend) he has killed and the others he will probably kill if he goes to Orochimaru. Sasuke wonders if other people's lives have stopped meaning anything to him, if his life has stopped meaning anything. Sasuke comes to a decision and starts running wild, tearing away, away from Konoha. He will not hear Naruto gurgle and gasp for air; Sasuke will cling to what's left of life (nothing) enough for the both of them.
It's not that life does not mean anything to him, Sasuke thinks, it's that Itachi's life means everything to him.
Without Itachi, there is nothing.
He thinks maybe it will be a good thing if he dies after killing Itachi.