I mean of course Sam is hurting too, but Dean actually remembers her. With him being so young, combined with John's stories of her, he remembered Mary as an angelic queen, and now he sees that's not true. Oops I just broke my own heart.
to be honest, the Boys don't get enough credit, think about it! Whenever one of them has been possessed, they essentially have to be TWO people at the same time, with DIFFERENT personalities with whoever they're being possessed by. MISHA ALONE.my gods.