Hello Bellabear
What a terrible situation to be in. In your shoes I would be angry too !
As much as your sister has been acting selfishly, and has made sure the world and the whole family were revolving around her, the most important thing you can do, is to accept your sister as she is. That does not mean you have to agree with the things she does or says. It also does not mean you don't have the right to be angry, because you have.
I will post you a link here, maybe you can have a look :
https://bpdfamily.com/message_board/index.php?topic=89910.msg604907#msg604907Radical acceptance does not even mean you have to stay in contact with your sister. It just means accepting that, unless your sister decides for herself to change, she won't.
Have you ever thought about it from another angle ? When your sister moves away, there will be more time and space for you to heal. You won't have to deal with the dysfunction on a daily basis anymore.
I also wanted to tell you that I completely understand the lonely feelings you are having. I also feel like an orphan, although both of my parents are alive. My mum is BPD, and my dad, well, he's enabling massively and might have some NPD traits. My paternal grandma is the only grandparent still alive and she's BPD as well. My other grandma died last summer and I miss her very much. I have a sister but well, let's say I suspect she's BPD as well. I don't get to see my FOO (family of origin) very often. And I guess that's for the best because they all cause me a lot of stress when I do meet them. Luckily I have my daughter, we have a wonderful relationship, she's the light of my life.
You are saying you don't know how to explain to your children that your sister is moving away. I think that moving away is not necessarily a BPD red flag (the way she's doing it might be of course, but that's something else and I suppose you are not planning to explain that to your children). Anyone is entitled to go and build a new life away from their FOO. As much as your children might miss their aunt, it's still a natural process and part of growing up. I think explaining that her moving away does not mean that there won't be any contact is the key. Try to not dramatise the move, since children easily spot our insecurities and pick up our grieve and frustration. I know I have projected some things on my kid that were actually my worries, not hers.
Do you think your sister will be willing to keep contact with your children by phone / by email ? I don't know how old your children are, maybe they can from time to time make a drawing that you can send to your sister by mail ? Making a drawing might give them the feeling that they can do something, that they can somehow control their situation. It's very active, in contrast with only feeling sad that auntie left.
You can tell your sister that your kids miss her, this will give her the feeling that she's important to them. You can also ask her to photograph her pictures on the wall of her new home and show them to your children. They will feel important too when they see them like that.
A few of my friends live abroad, I don't see them very often. But sometimes we call and then it feels like they are right next to me. One of them likes to talk a lot like me, and we can talk for literally hours. Sometimes when I put down the phone after a few hours it's like we actually met !
Do some of the things I wrote make sense to you ?
x