Winchester's Anatomy

Sam’s insecurity/fear is really interesting when you think about how hard that must always be for him. He thinks that Dean holds the stars and constantly sees how many people are attracted to his personality (Benny, Crowley, Charlie, Cas, Bobby etc). Sam knows how kind, loving, selfless and consuming Dean is and his love, and feels incredibly threatened when it seems someone may take his place. 

Dean is protective, Sam is possessive.

That scene, where the brothers are in therapy with Jack, talking about their mum’s (yes, I’m a Brit) death and Sam says, something along the lines of ‘who does she always go to for help’ my understanding of this line, beyond that obvious, that Dean as the older brother, had more of a real relationship with their mother, but Sam as we all know in this fandom is incredibly clingy and covetous of Dean and his affections, and knows what other people see when they look at Dean, because Sam sees it too.