Dean is exhausted and he's well aware that Sam is too. However, he suspects that Sam is having as hard a time sleeping as he is, so he doesn't feel too guilty about bothering Sam, especially when he's bringing whiskey which will probably help both of them sleep.

They've lived together their entire lives; Dean would be disappointed if Sam couldn't recognize his footsteps. "You can give me the highlights," Dean says as he sets the whiskey and the glasses down on one of the tables. He doesn't want to talk about the Brits either. Once Sam asks what's up, Dean takes that as his cue to pour a couple of fingers of whiskey into both glasses, passing one over to Sam before taking a sip of his. He sets his glass on a side table next to one of the big, comfortable chairs before dropping down into it. He grumbled and sighed then shook his head. "Just a lot of shit going on. How're you holding up?"

Dean had a purpose and a topic in mind when he walked into this library, but he can't just dive into it like an emotionally well adjusted person.