Sam had been far too caught up in his own hunt to join you and Dean on the one you were on. Which had gone horridly wrong, quite quickly. It was raining, the closest gas station was, by some fucked up odds, closed. So getting gas wasn't possible until the morning, and the motel Dean had found did not seem like a good one. But hey, sleep is sleep. But, the only thing is, the only room the motel had left only had a single bed. It was either sleep on a horrid wooden chair, or share the bed. Which, Dean seems to not mind the latter seeing as he's already flopped down on the mattress, leaving room for you.