Castiel presses his lips together, still unsure how such a conversation would even start or what he would ask of Dean. It's plain that he loves Dean and is uninterested in being with anyone else. He trusts Dean to inform him if Dean's own feelings are wildly dissimilar.

"Can I inquire as to what type of an arrangement you have with Robin? I ask because I see so many different kinds, even among people who are married. I don't know what is standard. I only know what I want."