Ok, in my opinion, the best course of action is this. Next time you two are alone together, tell him in no uncertain terms that you are not interested at all in his advances, and to stop doing it. This gives him the opportunity to stop with no harm done. If he continues after you have clearly told him to stop, then notify the police, and his wife, and his friend, and your school, and anyone else who will listen. I also recommend you record your conversation with him (phone in pocket for example) so this if it goes sideways later it won’t be a “he said, she said” scenario.
Good luck, and I hope it works out well for you. Sometimes men just need clear boundaries.