hi TakingCareOfMe21, and welcome to the family.
i had/have a hard time breaking up with people too. i probably threatened or tried to break up with my ex over a hundred times. i didnt do it, by the way. i was incredibly devastated when she did.
breakup/makeup cycles are generally damaging to a relationship. our loved ones are inherently distrustful, always afraid of the other shoe dropping, very perceptive, and their affections can wax and wane accordingly. and we withdraw, then reinvest, become exhausted...its a dance neither fully realizes they are in.
now, i assume that you are here because youre looking for hope, and for tools; that you love this person and want to make it work. having said that, im a firm believer that being emotionally capable of walking away is essential in any relationship, and especially in these relationships, i tend to think its best to be either all in or all out. if you walk away, do so for good. otherwise, with support, determine what is broken about this relationship, and how, and/or if it can be fixed, and commit to it.
swoe is a good place to start. it validates us. there are two good books to follow with. Stop Caretaking is a bit more about us, some of the things that we do that dont necessarily help matters (
https://bpdfamily.com/book-reviews/stop-caretaking-borderline-or-narcissist). and then Loving Someone (
https://bpdfamily.com/book-reviews/loving-someone-borderline-personality-disorder) is more about how to create the kind of environment where you, your partner, and your relationship can thrive.
i recommend all three, along with a strong support system like the one youve found