How to deal with this break up?

I’m trying to be firm with my ex boyfriend. Basically we’ve been going out for over two years but we keep on fighting. Every time we fight (and its usually over his ex girlfriend—the mother of his child) we break up and then reconcile after a week or so. Last week we broke up and this one stuck. Neither of us spoke for a whole week and then we spoke on Saturday and he said it was for the best and he was happy with it. Now he’s calling me saying he wants to get back together and can’t let me go. He was very upset and can’t understand why I don’t want to go back but to be honest I’m just exhausted. I can’t keep going back to him when fights like this keep happening. I’m trying to be the bigger person and do what is best for both of us but he feels like I’m betraying him.

His ex is very difficult and tries to stir up a trouble all the time, he can’t see the badness in her and of course I’m always nagging him about her. I’ve turned into somebody who nags 24/7 and I don’t even recognise who I am anymore. I explained all of this to him but his answer is that he needs the nagging to keep him in line. Basically, his ex is always trying to get back with him and he lets her walk in and out of his life as she pleases……..she’ll even call him and not ask about the child but just want to talk to him and they’ll chat away and he doesn’t think anything is wrong with this and I find it totally inappropriate. I’ve reached my wits end.

So now I’m not sure what to do. He keeps calling and texting but I think the best thing for us to do is to go our separate ways. I will never be comfortable with his relationship with his ex and I have to accept that she is around for the long haul. I can’t stay with him to make him happy because in turn I would be making myself miserable and stressing myself. Should I cut all ties with him or is it better to talk to him when he needs. I don’t want to give him false hope and I know I prob sound very unreasonable now but I have gone through a lot with this man and our last fight was just the straw that broke the camels back. I want to break this cycle……..help!