To be clear: Cullen isn't thinking about his sister.

But in that brief conversation -- it's as though she granted him permission to stop worrying about how they regard him. And now that he and Alistair don't have to worry about interruptions --

(And he's doing a fair job at not thinking about the impending certainty of Alistair's death.)

-- he's free to feel every part of what's going on, with no straying thought to give him pause. Cullen runs his hands over Alistair's back and shoulders as though to study the topography of his musculature, lingering on the small ridges and hollows that his scars create.

It's closer to prayer than anything Cullen's done in weeks. It brings peace.