Hi Janneke!
Welcome to our online family. What a relief you must feel to have finally discovered and found validation for all of those troublesome feelings that you've had towards your sibling. Now you know the 'why.'

Once you discover the 'why,' then you also begin to gain understanding into this disorder.
I was really, really sad when I read that BPD is uncurable. I am angry that I am going to have to live with this for the rest of my life.
There are T programs available that can help with BPD, but the pwBPD has to be willing to actually seek help. Many BPDs are not willing to do so because they don't think there is any problem. Do you think your sibling will ever consider T? Nonetheless, even if your sibling struggles with it the rest of his life, there are steps you can take to help you set healthy but understanding boundaries with him. The greatest challenge is in learning how to live with someone who has BPD and keep yourself healthy. I'll post some links that might be of help to you.
https://bpdfamily.com/content/ending-conflicthttps://bpdfamily.com/content/karpman-drama-triangleAre you home for a long break and struggling to deal with the drama right now? How old is your sibling? I'm so sorry to hear about the trauma he has gone through-was there any T to help?
Wools