It's a pretty long story that's from sam or dean's point of view(maybe?) that shows Castiel trying new things and learning how to live like a human because he is slowly losing his grace, but it takes the boys a while to realize that's why he is doing it.

One scene that I remember really well is Gabriel taking Cas to a chocolate fair or something and Cas being on a major sugar rush. Dean tells him that he should be bouncing off the walls not vibrating himself into oblivion and Gabriel said that Cas would take the house down if he started bouncing.

Thank You so much in advance.