Dean wouldn't say he's overprotective of his little brother, Sam. More just...curious about what's going on in his life.

And when he found out that his brother was seeing someone and his best friend, who knew, didn't tell him...he was livid.

"Castiel, c'mon tell me!" Dean said looking down at his best friend who he had pinned to his bed. "If you don't I'll...uh...i'll lick you. Yeah, I'll lick you!" He said with a smug smirk.