A friend of mine was diagnosed with BPD and I have a few questions about how it feels

Hello everybody! A friend of mine was recently diagnosed with BPD, so I read a little about it and had some questions. I don't have BPD, and I would be glad if you could explain to me how a person with BPD feels some things because it's conceptually difficult for me to understand it.

1. "don't have a strong sense of who you are, and it can change significantly depending on who you're with"

2. "Chronic feelings of boredom or emptiness"

I cannot imagine how it feels and has never experienced it, and I will be glad if you tell me about your experience and explain as much as possible. I just wish I could better understand how she feels and what she means when she talks about it.  
I would ask her, but is not the best time for these questions now.