Aren't you describing characteristic symptomatology of your BPD? And if so, being aware of why you have been in this cycle should help you develop healthier ways of relating. Say, you identify that event A has happened, e.g. the faintest sign that they won't always be around. Identify the typical response to events like that from your past. In your cycle, it is doing something that tests the relationship. OK, to stop the cycle, focus on NOT doing that specific thing. Do not test them. That is how you break the cycle, by focusing on specific segments of that cycle and breaking the individual "connectors" that, taken together, have made your relationships in the past deteriorate.