This was such a delight from start to finish, and what a finish! I was resigned to dead Snape (based on the warning) so was beyond glad to see he was given a choice.
The consideration given to Snape's inner, as well as outer, life when he joined the staff was particularly welcome. I've never read a fic that did so with the thoroughness you present here, taking everything, even his mindset, into account. I really appreciate that.
I also love the background you've given Filius here, who is one of the more unappreciated characters. The explanation for his duelling skills, as well as his generally unflappable nature, is genius.
The slow build of their relationship and the ease of it was as comforting to me as it must have been to poor Severus. I'll be re-reading this in future, I can guarantee, on those cold days when I need something to warm and cheer me.
One more thing -- this line? "Keep her with you always, but let the pain leave now."
I was mentally cheering even as I was swallowing a great lump in my throat. Brava!
I look forward to the reveals, in the hopes I am either unfamiliar with your work (and there might be more to read in some archive) or that I am familiar with it, but unaware of other gems you have authored. Thank you again!