Hi
I'm glad you found our site and that you shared some of your heartache with us. I'm really sorry that you are so overwhelmed right now. When you have a BPD in your life, so many things become much harder. From what you shared about your sister, it sounds like it is difficult to know if she is telling anyone the truth or not. What is her pattern in the past when it comes to being truthful?
Whether it is true or not that she has a tumor does not give her license to say whatever she wants. She may
think it gives her such freedom, but that is not reality. Unfortunately with a pwBPD, they do not easily change their behavior. You will need to take care of yourself in creative ways. Some of that will be boundary setting. Here are a couple of links to help you.
Empathic listeningSetting BoundariesYou'll find a lot of other members here that are in similar situations to yours and they'll offer helpful ideas and listening ears. We are a family here to help you. Have you read any books about BPD or how did you become aware of BPD?
Wools