Broken. It's the only word Oliver can use to describe Percy as he watches Percy stand over Fred's lifeless body. Percy is broken, torn to pieces by loss and guilt.
Oliver wants to hold him, to tell him everything will be okay. But he knows it's a lie. This isn't the sort of thing a person can truly recover from.
He feels helpless, knowing there isn't a damn thing he can do. This is one wound he can't kiss better, one tragedy that words and promises can never heal.