The first time I saw him blushing was on episode 3. You need to choose the basketball club, and than, there's a dialogue with Castiel. He says: Hey, where are you going? And you answer: I'll see a guy from the basketball team. Than, Castiel says "Probably, he's kinda boring" and you ask "Are you jealousy?" and he says "No.." and blushes *O* sorry, I only saw ya message today :/ hope I could help ya!