IMO, if Dean's at all aware of how Castiel feels, it's on a subconscious level and he doesn't really care. He's not being flirty or a tease here -- he just needs to get something done and he needs to talk to Cass at the same time. The fact that the "something" he's doing involves being stark naked is pretty irrelevant to him. That said, I think that Dean is very fond of Cass and when Cass thinks of the "way that Dean would let himself be loved," this is it -- Cass offers him a companionship and a link to the pre-apocalypse world that he can't get from anyone else, and that's why Dean likes him around. Of course, it could be that Dean will eventually get to the level where Cass already is in which that need for closeness with another person turns into a desire for intimacy. But he's not there yet, I think.