Dean never calls because even if he did Sam would never answer.

Aww, so sad ... all of it so sad. *sniffle* A great, moody piece. You nicely captured how horrifying if would be if Sam got possessed by that demon, how much it would torment Dean. The demon continually calling Dean is just chilling. To that end, this was my favorite line, because it's sad and creepy all at once:

Hey, Dean, it's Sam becomes the phrase Dean hates most in the world.

Thanks for a great read.