How do I get a clingy class acquaintance to back off without being too harsh?

So a guy from my aeronautics class who sits alone started sitting with me after I included him in a flight group that we only group with when we do flight simulators ( which we rarely do). Ever since, he's been super attached, following me around after class even after I say bye and try to walk away, He ask to sit with me and my friends at lunch, ask to walk me to my class, and just makes me feel totally smothered. My heart drops and beats fast when I see him, i immediately try to avoid eye contact and walk away fast. He's not my type at all and i don't see him that way, but i feel so bad because he has no other friends and new to the school. And honestly i lowkey resent him and his presence is starting to irritate me. I fear I’ve been a bit too nice and he maybe feels like I like him. How do i set a hard boundary and get some space without feeling like a terrible person?