Oh. Oh dear. What's not to adore here? There's my dearly beloved pairing, now even more precious, because of its rarity. There's intensity and madness and a whiplash from sudden mood changes, all trademarks for Snack. There's unhinged vulnerable Sirius (it is my personal opinion that drugs helped but a little, that's how he is) and mostly rational but still vulnerable Snape. There's Peter, portrayed in all his complexity, intelligent and scared and sensitive.
I must admit that near the end I froze for a moment when Pete almost accepted the burden of being the Secret Keeper. I've never been more happy to discover it's still an AU. ;-) I loved that during the masquerade you gave them each other's eyes. I loved your Bella and the much darker repetition of "Mudblood scene", this time with Sirius as a victim. I love that a fic which, with such a premise, could have started and ended as a light-note PWP (and I'd have squeed over it, don't get me wrong), turned our to be an intense, emotional story.
/Eeek. Seems that when I love I tend to lose control of my punctuation. Ballistic commas, anyone?/