Wow, this is really remarkable, for everything that's isn't said, but implied. The subtle suggestion of Snape's feelings and motivations are brilliant. I love that Harry has to tell himself over and over again that he hates 'the Quiet One'.
This bit: sometimes Harry can't stop himself from arching and twisting for more. It...it reminds Harry of early summer, in the shade of a tree, cool and green and nice. A Death Eater shouldn't be allowed to have magic like that. Wonderful. Not the sort of associations that one would normally make with Snape, and certainly not the sort that Harry ever would have expected to make.