What should i do?

My ex and I have continued talking despite me initially wanting to end all contact. We have the same classes and I don’t really talk to anyone so I had no choice but to talk to him. He’s very persistent in keeping contact and keeps on raising my hopes that we’ll eventually get back together. On the inside I miss and love him yet I know he was never treating me right. I still cry over him and I hate how much power he has over my emotions. I’m also starting to see him for how he is and not his potential. Do I explain my changing views of him to him? Because he keeps wondering why I’m being distant or dry. Its hard for me to explain to him the issues I have w him because he gaslights and gets very defensive so I bottle everything up inside. I know I’d have to cut him off eventually but it’s so hard.