Dean sees Sam in red, blood red, gasping and looking betrayed when he comes to. He needs to fix Sam, he needs to save him, every fiber of himself screaming save Sam. Dean steps forward saying “Hey, hey. It’s not that bad. Sammy, Sam! Hey, listen to me, we are going to patch you up, okay” and Sam flinches; he looks in hand and sees the first blade covered in blood. He is the reason why Sammy is dying,afraid of him, and he messed up. He killed his brother and now he understands why Cain picked him