okay but - an episode where a witch casts a spell on Dean and ironically it is a love potion, in which he acts all lovey dovey around everyone including his brother and “Jesus, Dean! Stop complimenting my hair you HATE my hair no no stop it go away!” and Dean is flirting with everyone and batting his eyelashes, and he can’t control it because he just doesn’t /care/ because he just feels so in love with everything and everyone -

and Sam has never seen this kind of spell before so he needs backup like, multidimensional wavelength of celestial intent backup - and so he calls for Castiel and “I’ve never seen anything like this spell before Cas! I don’t know what kind of spell it is or how to cure it and sure the spell seems harmless enough but he’s been talking to a pot plant for half an hour telling it how pretty it is and freaking petting it -” 

and Cas nods, and though it sounds amusing, he too doesn’t want Dean to be stuck in a mindset where he is incapable of any real thoughts and feelings -

so together they walk into the bunker to see Dean -

and

“Oh hey, Cas. Good to see you again, all suited up - back in the game. Where you been man?”

And that’s when Sam realises.

Dean has always been in love with Cas