I hope that title made sense lol. This is my first time posting here 

So like, I've been really frustrated with my best friend for months and my BPD tells me that she only wants to be friends with me because it's convenient - mostly because I have a car and she doesn't (we live together). It kind of feels like she uses me and whenever she doesn't need me I'm ignored. 
I know.. at least I'm pretty sure.. that's not true. but it's still like a nagging feeling I have and I'm honestly not sure how to bring it up to her as like "this is a concern I have but I know it's probably not true"
One of the biggest problem I've had since trying to manage my BPD myself (I can't afford a therapist) is if my feelings are valid even if they're a product of my mental illness. Because I still feel that way? Should I be upset?