This was haunting. I'm sitting here in a mess because damn this pulled at the heartstrings.
I didn't quite get the way the conversations flowed backward until I went and actually reread one of them backwards. You conveyed Harry's confusion and then loneliness wonderfully.
I felt so terrible for Severus at the end, but I felt worse for Harry at the beginning. (Wait, did I say that right?)
This story will stay with me for a long time, and that's the best compliment I can give.