Wow, this is perfect. Better than perfect even. It might be an odd thing to say, but I think I would have loved this just as much if it had been a friendship story. Snape and Firenze have such a sweet relationship, it seems very calming for Snape.
When I started reading this I didn't realize that it was also art. I can't tell you how amazed I was to be scrolling down and WHAM! ART FOR ME! And there's two of them! I love both of them to death. The way that Snape is clinging to Firenze, with him looking over his shoulder on the first one is fantastic! And I really love the dimples in Firenze's back on the second one. Did the same person who drew these write this story? If so, it's completely unfair that one person can be that talented. ;)