Wow, good twist of goals at the end (and thus he's failed again, right?). Sometimes you don't know what you have until you lose it.
I was intrigued and amused at several lines you put in this: making an unbreakable vow he didn’t intend to honor... I'd always wondered about that, b/c he made the vow long before Albus hurt his hand and asked for his help in dying, so what WAS Snape thinking?
no Gryffindor would have failed to leap so many times. wow, I'd never thought about it like that before.
He no longer knew if he was lying to Albus or lying to the Dark Lord. Surely either one would do. oh, god, that seems so true now, and both of them were just using him in return. so messed up.
After a long cold stare the boy has left him here. man, now I'm pissed at Harry. (good job, though.)
Really this packs quite a punch for such a short piece. Kudos!