Oh gods, this was fantastic! I really love the idea of Wishful Thinking as a magic itself. I love how Severus is almost obsessed, but doesn't seem to realize why it might be bothering him until Harry makes him see the truth. I love how he interrupted Harry's date like that and how Harry's date actually resembled Severus! It really came together beautifully when Severus saw naked Harry on the bed, then went to see Harry and found him doing exactly what he'd imagined.
And the ending! Soooooo hot! I absolutely *love* it. :D