sharlock,
It sounds like you are putting your needs first right now, and I commend you. It's not an easy decision. Since you will see your friend at work, NC is not an option for you, but you can control your side of the communication.
Here is some great info. about how to leave a partner with BPD. I know this isn't your partner, but the advice may be helpful for you.
Leaving a Partner with Borderline Personality Disorder How are you doing today, sharlock?