BPD for years was my own personal hell. Your friend is lucky to have a good friend. I was out of control

Self injuring
acting out negativitly for attention
In the hospital montly until they shipped me to a state long term hospital
Don't trust no one and to afraid of being abandoned to connect
Wanting so bad to be loved but pushing everyone away
Anger mainly directed at myself.
It seemed for a while my goal was to stay in the hospital where I felt safe

Stick to your friend because they will need all the support they can get. Even if they are pushing you away don't leave unless you are in danger.