My classmate had sex with his English teacher. what should he do ？

This issue involves ethics and laws, and different people and different cultural backgrounds may have different views and practices.

From an ethical point of view, sexual relations should be based on mutual voluntariness, equality and respect, not on power, control or interests. If this relationship violates these principles, then it is not a morally acceptable behavior.

From a legal point of view, sexual relations should be protected and supervised by law to ensure that the rights and interests of both parties are protected. If this relationship is regarded as a violation of the law, it may be sanctioned by law.

In short, sexual relations should be based on the principles of voluntariness, equality and respect, not on power, control or interests. If this relationship violates these principles, then it is not a morally acceptable behavior.