You broke up with him because the relationship wasn't happy. A relationship should build you up and make you happy, not make you live with drama and sadness. Evidently, Mr. Ex doesn't seem to think you've actually shut him out for good, otherwise he would not be contacting you to see you again. If you've broken up with him, it's past the time for a "break" for a few weeks.
If you don't want to see him anymore, and I don't think you should, text him again and tell him you want to see him about something important. You will need to have an end-of-relationship discussion with him to formally end things, otherwise he'll be sitting in a place between broken up and in a relationship with you. You will need to help him move on. My recommendations:
1. Ask him to get together with you to talk, because he wants to see you. (Do not try to break up by text.) When you do get together, to soften the blow for him, start out by talking about the positives in your relationship with him, but then move on as to why you don't want to see him anymore.
2. Make sure he understands that this is THE END. Be confident. Practice what you will say to him and try to anticipate what he will say to you. Practice with a friend, if you need to. I'm sure your friends will offer you much support.
3. Avoid cliches like: "We can still be friends." No, actually you can't focus upon dating someone else if you try to do this. Don't promise to be his friend. I've never been interested in being friends with exes, because it only keeps you in that zone between dating him and being an available single. It's hard to move on when you haven't totally gotten him out of your life. Jealous feelings might arise from him when you start dating somebody else. It's possible that at some point much later on from now, if you want to be friendly with him again, and if he is dating somebody, you can do that. But for now, emotions are too high and feelings of ownership are still there.
4. Make sure you find the right place to talk with him. Pick a neutral place where the two of you didn't share special memories.
5. Make sure the two of you are alone and free of distractions. You don't want this personal conversation to go on in front of others.
6. Now end it. Tell him that he will find a great girlfriend to share his life with eventually. There are a lot of nice girls out there who can date him.
The first relationship is the hardest to break up from. I remember it well. After you've dated several guys, you will come to the realization that for every broken relationship there is another one waiting for you. You have our permission to release your emotions. You want to let him go. Do it.