OMG, this is brilliant! I love it. I love all of it, from thinking the diary was some sort of matchmaking effort--serious, if something Cas didn't entirely understand--to realizing that it was a prank just as Dean was falling for Cas, to the heart squeeze of Dean finding out about the prank, to the utter relief and happiness of them getting back together at the end. And the contents of the diary are just hilarious. <3 <3 <3

Thank you so much for sharing!