I understand. My ex was BPD and the divorce aftermath of our difficult marriage was like nothing I've ever been through, a category 5 hurricane that lasted 4 years. Then I met and married my current H whose daughter has BPD.
Her personality is such that she has more quiet borderline traits and is not what author Bill Eddy (
www.highconflictinstitute.com) describes as a high-conflict personality (HCP). Eddy describes an HCP as someone who recruits negative advocates, has a target of blame, is a persuasive blamer, and has a personality disorder. You can have a personality disorder and not be an HCP, but an HCP typically has a PD.
A lot of people assume that BPD and HCP are interchangeable, and I'm learning from my experiences with SD22 that while BPD alone is very challenging it isn't nearly as destructive as someone who is also a high conflict personality. I have my ex husband to thank for that insight.
The one constant with both SD22 and my ex is with reality testing. For most people, cause leads to effect. Whereas with a BPD sufferer, effect leads to cause. SD22 chronically feels abandoned, but she does not seem able to locate the source for that feeling within herself, so she is constantly searching for the cause of it. If I have a pensive look on my face, that must mean I hate her. In her mind, she has located the cause (me hating her) of the effect (her feeling like garbage). If I say that the look on my face is about my son's recent surgery and my concerns about his health, she feels invalidated because then she must keep looking for the cause of her anguish within.
Her brain is different than mine. She does not think the way I think and that means using specific relationship and communication skills with her. She is more covertly aggressive than overtly aggressive, and I'm adjusting to that because shadowy aggression can lead to more self-doubt on my part. It's taught me to trust my instincts and be more assertive more consistently with her. Because I was married to someone who tracked the same way and feel exhausted by it, I limit my exposure to SD22 and no longer feel guilty about it. I cannot support her if my needs are not met first. Learning to define those needs took some time and it was worth the effort to figure them out.
That your daughter accepts her dx is a silver lining in all this. BPD is an explanation not an excuse, a distinction that may be difficult for her to understand but it's one that can help you when you're ready.
It's ok to take time to shore up strength and process the grief. I gave myself 3 years of dating H to decide if I was ready to wade into another experience with BPD dynamics and a lot happened in that time. You have that opportunity now with your daughter choosing (?) to live elsewhere, with someone you know and trust. And you had the wisdom to insist her aunt participates in therapy, which says a lot about your ability to put important safeguards in place.
It does seem counter-intuitive to focus on your needs when you have someone with such extreme needs in your life, but I have found self-care to be the source and strength of all the other skills. Not just bubble baths and yoga, but recognizing what it means to feel safe and rested and secure. Be the change you want to see in her, as corny as that may sound. To support her, your cup must be full, and you will need to become an expert in keeping that cup filled so there is enough left over to go around.
Posting here is a really good first step.