I don't really agree. Sam and Cas don't really have a friendship. Anything that Castiel does for Sam is only in service of Dean because Cas is directly Dean's friend. Also, if Cas was really Sam's friend, he would;t have broken his wall in the first place. That's not friendship. Cas used Sam as a pawn for his own agenda.
Re: MORE SPOILER DETAILS
I don't really agree. Sam and Cas don't really have a friendship. Anything that Castiel does for Sam is only in service of Dean because Cas is directly Dean's friend. Also, if Cas was really Sam's friend, he would;t have broken his wall in the first place. That's not friendship. Cas used Sam as a pawn for his own agenda.