I love the fanon that Dean drove Sam to the bus stop and let him go after Sam and John got into the "don't ever come back" fight, but I'm sort of equally in love with the idea that Sam left when Dean was out somewhere, unable to say goodbye. And I also think that much of the conflict between Sam and John arose from John's terror that something might happen to his son.

Thanks. I'm glad it stood up to a second read-through. :)