I don't know the situation, obviously (Geez - I just invited myself over ONCE - kidding). However, I find honesty is the best policy. In any relationship, we stress so much about how the other person is going to take it, but if we are just honest; it tends to be how it's meant to be. Maybe don't be cruel, but just tell them you don't want them in your life.
Hey, thank you for reaching out. However, I don't think it would be a good idea to catch up. You know we tend to fall into the same patterns as the past has shown. I'm in a good place and I think we are in a good place as we are separately and I would like to maintain that. --- yadda yadda.
Something that is all hey, I'm not interested but yo thanks, ya know. It's hard. I moved to a different state to get out of a cycle with an ex. We'd break up, stay friends, do things, end up together, be good, get toxic, get 100x worse than the last time, break up, stay friends.... So I understand. It is hard to walk away, but it's best for you and that should be honored.