I have his true friendship, and so he’s going to have mine. And as long as that is true, I cannot imagine what is possible.
And here we have Sam yet again with the "because it's Cas" phrasing. "Why can't i stab him in the neck like anyone else?" "Because it's Cas." Now: "Are you sure about this? I mean, it's CAS." It's like he's Dean's (and therefore our?) reminder of what Dean can't/won't say.