The aforementioned Snape fancing Cat-Head here. Yes. Yes, yes, yes. Much like you, I suspect that Snape was acting on a previously worked out plan between he and Dumbledore. I think it would be in character for D to sacrifice himself for the ultimate goal of destroying V, but the question for me is: Is Snape doing this for the greater good or is he doing it to take V's place? Forget "right" or "wrong" - what can the white hats offer Snape to rival being the Half-Blood Prince? And like you, I perfer a friendship between Lilly and Snape vs. mucho snogging. ;D