Hesitating just for a second, no, even a second was a long time to hesitate. It was enough time for loyal servants like Cocytus, Demiurge and Solution to show hostility once more. In that amount of time, Sebas came to a conclusion.
Sebas was Nazarick’s butler. He was nothing more than that. His foolish hesitation caused this situation. If he had asked for a permission earlier, this would not have happened. It was all his fault.