In the TV series, Sam had Sully as an imaginary friend because he was alone. Dean was off hunting with John and he found himself a different support system. In Brothers Together, he has Dean around all the time, and in Brothers Apart, he went straight from having Dean around all the time to finding a new family. Sully helped guide him to figure out that he didn’t want to be a hunter as much as he thought, but that was never an issue in this series.
Brothers Apart 