So Castiel is having a showdown with some badass rogue angel and he brings up Cas's love fore Dean. And teases Cas about it, and says things like 'The Winchester boy is only using you. How easily you can be manipulated by such a pathetic creature."
And so Cas gets angry and after a bit of wrestling, offs the Angel's head.
But he's still upset about what the angel said because he realizes that Dean is pretty much in charge of their relationship. So Ca spoofs back to the motel room, teleports Sam away, and jumps poor confused Dean.
And Cas leads that night. And Dean is totally ok with that. And after Cas's aggression and upset is…. Appeased. Dean is lying there with Cas on his chest, stroking and playing with the Angel's hair, and Dean asks Cas why the sudden hunger for the lead?
And Cas just sighs contently. He had reassured himself of Dean's love because 1) Dean let him take the lead. 2) Dean was showing concern. And 3) Cas may or may not be spying inside of Dean's head for a moment. But while he was or was not spying, he may or may not have felt some of the rawest, strongest love and faith he'd ever seen since his own love and faith in God had been pure.