A bestfriend should always be there for you when you need them the most. That's what Caleb's for. He's Dean's best friend and will be no matter what happens.
When John died and Dean was a broken man, but Caleb was there for him.
"I'll always be there for you deuce. Right when you need me."
"Thanks Damien, I can always count on you."
"Best friends?"
"Till the end"
Well I guess it's a good thing that Dean has Caleb right?
