theres an questline surrounding the classroom harasser thats probably limiting your relationship if you havent progressed far enough through it, its a very dom/sub route that involves either visiting his workstation after class in the evenings or complaining about him to the teachers, depends if you want to be his dom or his submissive.
If you dont want either, id recommend taking the submissive route and just talk to him about "discussing your relationship" and requesting what kinda realtionship you want