There’s nothing you can do really other than be honest with him. Tell him you’re not interested and that he should move on. And hopefully he will.
I don’t know how old you are, I don’t know what you’re like as person, your gender, anything, but if I could tell you anything it’s give it time. Don’t force yourself to become something you’re not just because you feel like you should “be someone”. I’m 19 years old and I’m still not 100% sure of who I am. Question your and other peoples morals to figure out where you stand religiously. Experiment to find out what you like sexually. Listen to different types of music, watch movies that other people recommend, so places by yourself. Start a journal, document everything. I hope someday everything makes sense.