My Ex's is acting immature and a bit crazy

So about 2 weeks ago I broke up with my BF. We had been together for more than I year. I'm an 18(f) and he is an 18(m).

He was very controlling, and wouldn't let me live my life. After trying to leave him for a very long time I finally did it and I feel great. I don't miss him at all. I am the happiest I have been in ages.

He is convinced that we are meant to be together. He is certain that in the summer we will get back together. He keeps texting me, and messaging me on facebook. He also constantly bothers all of my friends about me.

He still says "I love you", and "I'll never find anyone else". When I told him he would find someone else eventually he got really offended. I told him he is being immature. He says he knows he can change and that if I still love him we will get back together after school ends. I told him that this will NEVER happen.

He says I am being cruel by avoiding talking to him. He wants to hang out with me in a few weeks, I said no. Then he threatened to come up to my University without my permission, so I said yes I would see him to stop him from coming here.

I have stopped responding to his messages. I don't know what else I can do about it. I've realized that no matter how many times I tell him we will NEVER be together again, he just doesn't get it. I told him he's hurting himself and being difficult, he says he's not. I just want him to leave me alone. Any advice? thanks!

TL;DR: My Ex who I broke up with not long ago won't leave me alone. He is constantly trying to contact me and says he is in love with me, and that we will be together again soon. I think he's delusional, and I don't know what I can do