Desire to reingage with past partners is very do able, and can be successful. I have done it twice with two ex. Both wanted to restart the relationship. The amount of work, showing them love and honestly not expecting anything in return is doable. It's something looking back to only do with a Simi healthy ex. The one ex after q year of showing love and friendship out of the blue, was ready to pick up where we left off. Realised she was better off just as friends, she learned a lot from me and is now married. The BPD ex , the same, she called one day, asking to move in. Unfortunately I expected love in return, that she couldn't understand. Look it's ok, to do these types of behavior. Had three sisters, all the guys, who hit, stalked, revenged, responded with anger, left them justified with their bad behavior, in the end, men who they called pathetic were eventually painted white were treat as friends after many years and made them more humble in the end. Please don't be hard on yourself for these actions. Your a good guy, responding the best way you know how.
Bingo! Any attempt to reengage with a BPD ex will be her opportunity to just stab you through the heart and push you away yet again. Don't try it, it will always fail. These attempts to reengage only work with healthy people who have compassion and empathy, traits which BPDs by definition lack.