Wow... That was certainly emotional. I love how Severus saw it as fantasy on Harry's part, and quickly leaves, only to be chased and caught.
I love that you used cannon compliant background stories of Severus's past for his reasoning as denying himself. That was truly remarkable, and favorite parts of mine. Poor Severus. The part about the Potion Master's purity of essence was ingenious as well.
I thought it was so powerful for Harry to "invite" of a sort, Severus into his mind through Legilimens, as we all well know how much Harry hated having his mind invaded during the series.
It was so sweet to see Severus develop feelings along the way, having been such a protector of sorts to Harry for years. I absolutely loved this one, and it was so much packed into such a small package of just a few thousand words.