Hi and welcome.
Also, I've sworn to her that I won't tell anyone and therefore cannot make them understand..What can i do to make the situation better?
I would keep my word and not tell others. What do you want others to understand? Her behaviors?
You ask what you can do to help. Generally the best thing you can do is to learn about the disorder and learn tools and tips on how to communicate better with a pwBPD (person with BPD). Also knowing and understanding there is little you can do to get them to want help. They have to want that on their own.
Can you give us a few more details about this person? What is your relationship to them?
As you share more, we can better guide you. In the meantime, we have lots to read here, check out the topics tacked to the top of the board.
