$tranger$ for ca$h
I interpret thus: When Dean says "we" it seems like he means "we = Dean, Sam, Cas" but actually it's "we = Dean and Cas". Similarly when Cas says "you" it seems like he means "you = Dean and Sam" but actually it's "you = just Dean". There's a miscommunication going on, between Dean and Cas, and between them and the audience. Different layers of meaning. The mixtape scene is a great example of this, and the argument they had just beforehand. I encourage you to watch again and interpret both ways.