"Dude... She pretty much told me she was in love with him. And then I left her to die." Sam felt pretty damn crappy about the whole thing. Sure, Meg had killed people they cared about and tried to kill them on plenty of occasions, but at the end of the day she had been one of their most loyal allies outside of family.
And she had listened to him. Way back in the beginning when they first met, she had listened to him ramble on about Dean and their dad and being dragged along despite not really wanting it. And now she had listened to him rabbit on about giving up hunting for love and all that went along with it. She got him. She understood him.
"She sacrificed herself for us man... For Cas. Where the hell is he? He should be here. We're his family."