I mean was there really any question about this. You can take it as Destiel and/or TFW, but either way he said it. Finally someone said it. More than being family. More than needing one another. Love. Cas loves Dean and Cas loves Sam (and I guess Mary maybe?) All the feels were felt. This is the line that we will be talking about for a long, long time!
And of course, as an added bonus I have included Dean’s reaction. Because, although Cas said “I love you. I love all of you.” The camera ONLY cut to Dean. Both times.
There is no way this line isn’t the “Best Line” of 12x12