Crow is distraught after his confrontation with the Nightmare of Uldren Sov. Being confronted by a manifestation of his darkest fears and greatest failures has crushed his spirits.
"We're exactly the same, down to the instincts. It's in my blood," Crow says, unable to reconcile the pain of his past.
He won't be able to perform the ritual of severance in this state. You should seek Eris's guidance at the Crown of Sorrow.