It's obvious that Castiel is nervous. He's not a good enough liar to hide the signs of that, and it's only natural. It's his first time, and omegas are under a lot of pressure to do well, do please their mates - those raised in very conservative households more than others.

Castiel prays that he won't accidentally cue Sam in to the fact that he expects it to be painful, though. He doesn't think he wants to hear it confirmed before he experiences it.

They're silent all the way up to their bed chamber, and even then when they step closer together, kissing softly. Castiel wants to get it over with, but at the same time, isn't so eager that he'd rush. So he's content to kiss Sam for a while before dropping his hands lower and reaching for Sam's belt buckle.