Welcome back!

I would confirm that you're not disordered with acting-out BPD traits. (Your situation and even your manner of writing indicate that.) Yes, you probably do have some issues that allow you to return to this dysfunctional on/off dance. Are you seeing a counselor? While the peer support here is so helpful in dealing with the impact of Borderline trait relationships, local in-person guidance and introspection is invaluable for
your own issues too.
One reality I've learned here is that past history is an indicator of future history, unless you change the dynamic. So something needs to change in order not to repeat the past. It takes two people to have a relationship. Since you can't count on your ex to change, then that task is up to you.