Hi scarlet, I hope you are feeling better today? It's hard to let support in if you have never had any. I can imagine with bpd that the feelings of rejection are magnified and this must be very painful for you. There must be a process in all of it. Have you ever tried to track your process and identify the triggers?
When you say you cried and had a breakdown, I am hearing self regulation is very hard for you and of course it would be if you have had no support and had to deal with these feelings alone. You maybe try to suppress them but the are so strong and powerful and just need someone to sit down and acknowledge them with you
I used to struggle with overwhelming feelings too, hard feelings I had never shared with anyone until my current t and even just saying them out loud. Like, "my parents never loved me" or "I am completely alone". They stopped screaming inside because they had been heard and acknowledged. I invite you to acknowledge your feelings that were crying for attention Scarlet. Really listen to what they need, or what you need and deserve.