Dean used to enjoy the little things. All of them. Like how full of pride his father would be after his boys finished a hunt. All the long car rides with Metallica or Motorhead blasting half the way to another job, the other half spent talking to his little brother and dad. Like how every single time he got shot-gun, no matter how much Sammy complained. How proud he was of his little bro for being able to balance school and the hunt, and be good at both of them. Like how good the sun felt when it shined on his black leather jacket he received from his father. Whenever he could relax at the end of a long day and drink a beer, allowed by his father because, well... hunters didn't follow the rules of society.
But when Sam went away for college all that changed. He just wasn't the same. It was as if half of him was missing and he was left trying to figure out how to make himself whole again. His brother was there and then he just wasn't. Dean had never been separated from Sam for long and at that moment he had no idea when he'd ever see him again... IF he'd ever see him again with the way he stormed out of their motel room after the fight with their dad. With his younger brother gone he didn't feel right. Thousands of miles away Dean couldn't protect him from ugly sons of bitches like the thing that killed their mother, watch him, stick up for him, or pick on him. He couldn't do anything. It made Dean feel even worse that Sam didn't call him either. After all, it was their dad he was on bad terms with, not Dean.
He didn't know what to do about the situation so he did what he does best... Fucking, drinking, following his father's orders without question, and killing evil sons of bitches mercilessly.