How do I leave??

I’m currently in a relationship that I feel is very toxic but everytime I break up with him and leave he always finds a way to contact me and once we end up talking I always get convinced that he’s gonna change and end up talking to him again. He can’t go a day without me and I wanted him to change and he is but very slowly and he is very closed off but I’m a very emotional person and can’t do this anymore. DOES ANYONE HAVE ANY TIPS ON MOVING ON??!