Castiel teleported himself in the direction of the kitchen and collected a bottle of whiskey along with two glasses. Sam may have been reluctant to drink, but since it was not customary to drink alone and common courtesy according the Internet, Castiel was behaving accordingly.
It was strange to think of human protocols in the face of Dean's disappearance but he didn't know what else to do. To have something else to focus on was helpful, but not necessarily something conducive to what he needed to be doing. Which, admittedly, he was still at a loss for in general.
He set the glasses down on the coffee table and poured Sam's glass first. "In order to know for certain, you would have to tell me," Castiel pointed out heavily. "I could take the thoughts from your mind...but I imagine that would be rude."
Dean had been quick to point that out to him. And at the moment, avenging the person in question seemed like a suitable course of action. No matter how irrational it seemed.