Hi. I want to preface this by saying I am not diagnosed with BPD, but the experiences I have are very similar to some things I’ve read. I am not someone who self diagnoses, and I am not claiming to have this disorder, I do not want any speculation on that, but I don’t know where else to turn. 
I am having a complete meltdown. I have been experiencing something that seems similar to the “favorite person” symptom ever since my childhood. I have been friends with this person for nearly 10 years, but I still can’t shake this fear of abandonment. They don’t message me back for 20 minutes? I’m losing my mind. Perhaps it’s anxiety, but it feels like much more. When I say I’m losing it, I mean I’m crying and immediately trying to cope with my life now that they’re “not in it”. My feelings about this person are very extreme. I find myself being extremely toxic toward this person but being unable to stop myself. I flip flop from being in love with them, only wanting to be a friend, and hating them more than anyone else within hours. It’s exhausting. 
I am an extremely straight edge and reclusive person. I don’t drink, do drugs, I rarely go out, and I follow the rules. I am not against anyone who does this- except when this person mentions it. She is also very straight edge, but mentioned a few weeks ago she wanted to “try drinking” and it sent me into a spiral. My mind wandered, assuming that this was her card to finally get rid of me. She was obviously going to become an alcoholic, find some hot boyfriend, and get rid of me. Now, a few weeks later, she’s going out with her friends. But she’s refusing to tell me where she’s going. I’m trying not to be pushy about it, but in my head I think she MUST be going to get drunk and so drugs to prepare to throw me to the curb. And I’ve been going through so many emotions about it. I’m sad, anxious, angry, and just sick to my stomach. I want to run and grab her and take her to my house and have her for myself because she’s my friend. But I also want to scream at her and tell her to get lost because I should be her best friend. Logically I know I’m being very irrational and toxic. But my feelings are in control and I can’t stop it. I mean, she hasn’t even told me where she is. She might be at a park or aquarium for all I know. But I’ve been crying for nearly an hour now because I don’t know what to do. I am so terrified and my thoughts are intrusive and spiraling. I know I can’t boss her around and control her, she can rightfully do whatever she wants. But it hurts so bad. I don’t want to be abandoned. If I’m gonna get abandoned I want it to be on my terms. I want to get rid of her before she has the chance to get rid of me. 
What can I do? Does anyone know what can help me cope? I am miserable. I had to call out of work today because I kept feeling like I was gonna throw up, I’m having a complete meltdown over it.