OH MAN I JUST HAD A THOUGHT. This whole season has been about putting Dean and Cas on an equal level. If you look at seasons 4-6, their problems mainly came about because they idealized each other, and when they didn’t live up to the idealized standards, their relationship suffered.
And being different species has been one of the biggest hurdles in seeing them as equals: Cas is more magically/physically powerful (being an angel), but in the TFW dynamic, Dean had more power as the keeper of social/human knowledge. And even when Cas became a human (or a hunter in 8x08), he floundered for a bit, having no power in this new situation.
BUT even from episode one of s9, Cas and Dean have been on parallel journeys that (I really hope) end with them on equal footing.
Castiel has been trying to figure out what he wants out of his existence, making the most out of the volatile situation and his changing species twice this season. As we see in 9x10 and 9x11, his time as a human, and subsequent re-angelification has made him understand humans, and more-importantly human emotion, better. He’s starting to get the physical language of humanity, with touches and hugs and sex. And with this episode, he now shares a common storytelling history with humanity.
Dean has also been moving toward seeing Cas as a person with feelings, rather than a blunt instrument (sidenote: this progression has been slowly happening in starts and fits since 7x17, but it’s been kicked into overdrive this season).
The times we’ve seen them together haven’t been them fighting monsters together (except 9x06). They are not using each other for whatever gifts they have defeating things (Castiel is very decidedly NOT Dean’s weapon this season), but instead when they are together on screen, or talking to each other on the phone, they have been shown to be each other’s friends first, allies second. In 9x01, 9x09, 9x10, and tonight, they provide emotional support (“How are you?” is asked IIRC in each of these episodes) and show that they really care about how the other is doing, and not just in the fight against evil. Cas cares about Dean’s state of mind and Dean cares about how Cas feels about being a human or angel again.
So as of this episode, Cas (more or less) gets Dean’s pop-culture references, one of the defining characteristics of Dean’s personality since s1. Now, Dean cares about Cas’ feelings and choices, letting Cas make his own decisions. 9x03 and 9x06 show us that they want to be together in some way or another, and I’m looking forward to them getting together on equal footing, making fully informed decisions to stay with each other without undue burdens of responsibility toward family weighing them down.
"keep an eye on him. keep two eyes on him. send me photos with your camera phone. i know how those work now. i will expect hourly updates sam make sure he eats enough vegetables you know how he is. make sure he has enough blankets."