Dean could be a real idiot sometimes. Part of the reason Sam kept getting sucked back into this life was the job. Saving people. Hunting things. The family business. But the main reason was because of Dean. There were plenty of times when he wanted to murder Dean - but what baby brother didn't want to murder his jerk of a big brother at some point?
But more importantly, Dean was the one who had practically raised Sam single-handedly. How many big brothers would forsake their own childhood to take care of a bratty little brother? How many big brothers would sell their soul to save their little brother?
Even if Sam had gone to Amelia, part of him would always be wondering if Dean was safe and every time the phone rang or he got a text message he'd be wondering if that was the call to tell him Dean was dead.
He dragged himself over to the sink, hovering over Dean as he held out a bottle of beer for him. "Here."