He has been incredibly good throughout all of this.
He is about to stop being good.
He is about to change the scene.
When she first came to him, he had been good. He figured out almost immediately what she wanted, but he restrained his usual sarcastic impatience, and gently guided her to her confession. With some self-interest, to be sure; but also with a genuine, if grudging, concern.
When she finally admitted what she wanted him to do to her, he wanted to comply immediately: to shove her over his desk, to shove her skirt up and her panties down, to punish her bare bottom until she cried. He has known her for years — the last few of those years spent trying to set aside the sordid thoughts he had about her, knowing it was unforgivable for a teacher to even think of a student that way. And now that she was offering herself, now that it was no longer morally repugnant to take advantage of her, he wanted to do it at once, to cruelly violate the young, vulnerable flesh that was being offered to him on a silver platter. But he was good, and while he had to bite his tongue many times, he talked her through her circumstances — the too-early marriage, the well-meaning dolt of a husband, the recent separation — to help her make sure she wasn’t acting rashly, and was making the right decision in coming to him.
And when she looked at him tearfully after their long conversation and said, “Can we do it now, please?” he wanted nothing more than to grab her by the ear, and drag her over to his desk, and show her exactly what it was she was asking for, and make her sorry she had ever asked. But he was good. He talked her through the negotiation, introduced her to limits and safewords and whatnot. And when they were done talking, he summoned all his self-control, and said, “You should really think about this. If you still want this a few days from now, then we’ll proceed. Are you free a week from today?”
And then, when she came back a week later, exactly on time, he was very good indeed.