The rest of his shift only flies by because he buries himself in his work. Derek doesn't come back, which probably means he went outside, got some fresh air and realized that Stiles is a mole-spotted, skinny weirdo.
It shouldn't hurt as much as it does, really. It's not like Stiles ever thought he had a serious chance with Derek but that didn't stop him from coming up with silly situations where it might work out; running into him in one of the hundred little corners of New York that Stiles frequents and striking up a conversation, maybe asking if Derek would mind re-locating to a bar or his apartment, maybe.
Instead there's only the knowledge that once Derek actually stepped back out of the Veela hormone splash zone he realized he was making a mistake. People like Derek don't ask people like Stiles out.
Even though his flu is gone, he curls up in front of another episode of Planet Earth that night and falls asleep on the couch before ten.