Welcome!
It is true that our BPD adult kids are living in an alternative reality that is real to them. It is very heartbreaking , but do not feel guilt. You didn't cause this. You took a good first step in adding this forum to your network of support. Please feel free to look around here . Pull down the tools on the drop down menu. I recommend you learn about BPD , look at the suggested readings in the Library on this forum. One good book is "Stop Walking on Eggshells".
It is very painful when they become estranged with us. I am also estranged from my adult BPD son as well.
Here is a link on estrangement
https://bpdfamily.com/message_board/index.php?topic=296973.0You are not alone here.