Snape's not the type to be just mean for the sake of meanness.
by Taulai
He's just not painted that way.
Yes, he's sarcastic and biting and can be downright nasty. But when he's really put on the spot, you get the strong sense of real pain.
But yeah. I have to agree that it would be far too simple for him to have just had a thing for Lily. There's more to it than that. And I'm betting, too, that JKR will have a rip-roaring good time with it.