The Joy is in The Process

Sam and Dean have never met anyone as unique as Castiel. The kid wearing a trench coat in the middle of summer introduced himself the day they moved in, and all three of them became instant friends. Then Dean and Cas start spending a lot of time together and Sam finds himself excluded. He doesn't blame Dean at first; it must be hard being fifteen and never setting down roots long enough to make lasting friendships. But as time goes on and he sees less of Dean and Cas, Sam realizes it's even harder being eleven.

Originally written on September 16, 2010 for the Secret Angels IV fic exchange, for recipient "writingpathways." I combined two requested prompts -- AU where there is no supernatural and Dean/Cas have been best friends forever, and Sam POV of the evolution of Dean and Castiel's relationship.