What I'm enjoying most about this fest is seeing poorly realized characters come to life, glimpsing their humanity, and viewing the world from their perspectives. This is my favorite fic so far for those reasons; I never knew who Rabastan was before reading your story, and I've learnt something new about Severus, as well. This is so lovely, and I can't praise the welcome smooth richness of your use of description enough: I feel as though I fell into a Pensieve reading this, a Pensieve containing a particularly vivid memory.
The only slightly jarring bit was your final line; it seemed out of place because it was from Snape's perspective. Rabastan's final thought might have been more effective, to my mind—but nothing takes away from the inherent naturalness of your presentation. I'm so pleased to have read this story. :)