is BPD learned or hereditary?

i don't really know the answer to this. i'm sure there's some big medical explanation on one of the bpd websites. however, i'm beginning to think that it may be learned. a lot of people in my life have abandoned me over the years, so maybe i have learned that it doesn't matter who you are, you will eventually abandon me. is this why i am so worried that my boyfriend will eventually abandon me and i will never hear from him again? every time he steps out the door i become completely scared that he will leave and i will never see him again because he will realize that he doesn't actually love me. even if he says he will be back later i never believe him. i guess my ultimate fear is being alone. nobody wants to be alone i guess. but i feel like i would not be able to function if i was alone.