It's so subtle and sweet and slightly perverse that I can honestly see it happening. There was nothing overtly fluffy about the story, but everything read so tender and genuine. Even the ending was perfect - I can't help but wish for a happy one, but fortunately you chose the better one. Perfect.
I'm sorry this is such a short response, but if I let myself go you may not be able to read through the fangirl-babble.
I intend to rec this far and wide. I'm actually re-reading HBP right now, so this'll add a new level of fun ;)