Make it clear to him that people should pay attention to convincing others with virtue, and don't use violence to solve anything. Violence can't solve problems at all. The first thing is to make it clear to him that he will not move if he does not move. Where you sit is your freedom and he can't interfere. If he wants to confront you or something, please ask the teacher, because some problems can't be handled by yourself. You think it's useless to find a teacher. Will you succeed if you are bullied like this? At least let him know that you are not easy to bully. Never mind your promise. If you are not afraid of shadows, you have nothing to promise.