This is so incredibly raw and kept me very immersed and *in* the moment throughout the entire story. I love how self-aware Harry is in this. It seems obvious that at that particular time in Harry's life, he'd be very self-aware--having just walked to his own death and having to mull over what the reevaluations of Snape's memories mean to him. I do think Harry would see the likeness between their situations--and relate. He's overall a good hearted boy/man who tries to do his best, even though he is by no means perfect, and I think he'd have been totally fascinated by Snape at that moment in time.
I also adore your Snape--he is so often portrayed in fanfic as nicer looking or just 'nicer' than he is in canon. (Although I do wonder if he played up the nastiness of his appearance and demeanor to help with his double-agent duties, I doubt he was secretly handsome and sweet in his true persona.) Your Snape is almost meaner than JKR's...but for someone who is so at sea, having lost his purpose and being confronted by Harry as he is here, your Snape's reactions read as terribly realistic. Of course he would not see himself as anywhere near good enough to have any sort of good will from Harry. You have a massive talent for showing the raw wound of Snape's psyche here and exploring how Harry attempts to sooth it, as well as Snape's reactions to that. (I did wonder though at Harry's intelligence at keeping the poor sick man out in the cold rain!)
This was just brilliant and very effective at keeping me completely engaged throughout.