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Obviously the writers left it open to interpretation so you could view Castiel's confession as love from a friend but if you view it as one-sided pining, it actually creates an interesting dynamic. It makes him the villain in a wincest fan fic type scenario.
All the times Castiel has hurt Sam- breaking his wall, leaving him to die, etc- suddenly look like an attempt to get Sam out of the way. When Castiel imitated him by doing shit like letting Lucifer in, it seems like a SWF move to get Dean to love him like he does Sam.
I don't know if they even realized the implications there but I'm interested in his character for the first time in ages. It makes me think about all the "Castiel is the real bad guy" takes and want to write a fic about it. Which I'll never do because lazy but still.
I'd write it from his perspective leading up to the point in the last episode where he sees Dean essentially throw the world away for Sam AGAIN and knows he's no farther along than he ever was so the choice to sacrifice himself is easy.
