Hi zipline,
I'm so sorry to hear about your breakup. These are often extremely painful and confusing separations. I went through an agonizingly painful breakup myself, and my ex also broke up without warning and disappeared from the face of the Earth. So, I can understand something of what you are going through and how hurtful and confusing this experience is. I can honestly say it's been the worst experience of my life. You're in good company here, however. Everyone can understand how hard this is and we are all here to support you.
I guess I want to know can a BPD person maintain both close and casual friendships, and only really be symptomatic in intimate/intense romantic relationships?
My exgf seems great at being friends with people, some extremely close, and having casual lovers, but the closer we got, the more unstable things became, the more irrational fears and accusations surfaced (I didn't care for her, I was still involved with my exgf, I was hitting on her friend, I was trying to sleep with her roommate, etc), the more words got twisted around to the point where I was afraid to talk about anything for fear of setting her off. She alternately loved me deeply and blamed me for all the problems and bad feelings she had.
This is a great question. The reason is because it is emotional intimacy that triggers the disorder. Often higher functioning people with BPD (pwBPD) are able to have successful careers and maintain a group of friends and acquaintances, so long as there is a good degree of separation from deep emotional attachment. These relationships are rather superficial. Romantic and family relationships, however, are by nature much more emotionally intimate and these are where BPD truly shows itself. Often other people may have no idea that something is wrong, because they do not see this side of the pwBPD.
The reasons behind this fear of intimacy are deeply rooted in the nature of the disorder. pwBPD had a tragic failure occur in their emotional development while they were very young in life (first few years). As a result of this, they have not been able to develop an autonomous "self". As a result they spend their life looking for attachments to fill this void inside of them. They look for someone whose self they can fuse with and thus hope to become whole. This is impossible, however. It can't complete the pwBPD, and eventually this breaks down, and that's when the trouble begins. Due to the unhealthy, unstable nature of this attachment, pwBPD experience terrifying fears of abandonment and engulfment. The fears of abandonment are the overwhelming fear of losing a self through loss of the attachment and return to the frightening and chaotic period when they are all alone in the world without anyone to soothe or care for them. They are the abandoned child, helpless and alone in a scary world. The fear of engulfment is essentially the opposite. It is the fear of being swallowed up and consumed by the self of the attachment. It is the entire loss of the embryonic, unformed self, and this triggers terrifying fears of annihilation. As a result, pwBPD seek to escape the attachment and thus hope to preserve their tiny, largely unborn self. It is these dueling fears that propel the push/pull cycle of the relationship. It explains why at times your ex so yearned to be close to your soothing presence, and at times pushed you away for being so cruelly controlling. Of course, this is not actually your fault. It is a product of the disorder.
It is so important to remember that this isn't your fault that the disorder was triggered. You are not the cause, only the trigger. And it is not your fault you became the trigger. It was in the cards from the very start, and sooner or later it was bound to happen. This is the tragedy of the disorder. So, please don't think that this has anything to do with what you did or didn't do, and don't ever think that it is because you weren't good enough. If you hadn't been so close and so cared about, the disorder would have never been triggered at all. It is because you were loved and special that the disorder became activated.
I'm sorry again that you are going through this. I can only say that it will get easier as you go along in healing. For right now, take good care of you. Try and eat well, get enough sleep, get some exercise, and do be very gentle with yourself. You are in deep grief and you have been hurt in a core way. Healing will in time examine that hurt, but for right now focus on being good to you. Taking care of you. You deserve it. Also, keep posting here. We are all here to support you. This forum was invaluable for learning more about the disorder and for proving such needed support during my own breakup. You're not alone.