As always the boys are not mine but Kripke's and I will fight him in a vat of lime jelly anytime he says the word!
The word is passion.
Sam watches and smiles when he sees how hard Dean tries to hide his true feelings.
To a stranger it would be an effective concealment.
But to Sam, who knows him so well, Dean is near transparent.
The signs are small but un-missable.
When he looks at her his breathing quickens and his pale green eyes widen in impassioned dilation.
They all pretend that the other knows none of this but Sam loves to see Dean's shy hand seek hers as they go about their gruesome business.
He longs for his brother's joy more so than Dean would ever dare.
Hope you enjoy!