"My brother's a Beta and used to dealing with Omegas who may be having difficulties. He'll make certain Castiel gets back to his room safely." Sam shifts his stance slightly, the protective instincts that Castiel's whine had brought up in him manifesting. "He's only doing what's in Castiel's best interests."

Since it seemed like Sam and Dean were the only ones in the house that had his best interests in mind.