Cas become Dean’s heart, his soul (Ironic, isn’t it — the soulless angel, as the heart of a man?) Without Cas, Dean loses his humanity, and so now, topside, he is a finely honed blade, a killing machine. He is the weapon both his daddies trained him to be.
We are watching the equivalent of Soulless!Dean right now.
BRING BACK CAS NOW GODDAMMIT
I CAN’T TAKE MUCH MORE OF THIS