Harry told Snape that Lily only liked James because of his money and looks. So is it that Snape now thinks his students only like him because of his position and power, whereas before he thought they liked him for who he was? Has he become even more cynical? More inclined to reject people?

This is what I figured. And there was the comment by Dumbledore (or Minerva?) that Snape wouldn't hurt Harry because Snape loves Harry's mother. So I'm now assuming that Harry managed to convince Snape that Harry's mother is not love-worthy, which means that Harry is now stripped of that protection.

ETA: Some reviewers thought it was a reference to Snape performing Legilimency, but of course it doesn't take a mind reader to notice a dreamy-eyed girl.

He tells her to stop staring at him, and doesn't look at her when she comes to see him after class. Perhaps this was because he no longer needs to read her mind, because he's decided to stop reading students' minds, because he was doing so at the headmaster's bidding and he's broken with Dumbledore.

Wildly conjunctive and supported by a hair's breadth of evidence, but I don't have a better guess. Nothing else seems likely to have a dramatic effect on Harry's story.