Welcome AndreC!
I was just about to get off the computer and try to sleep when I saw your post thusfar unanswered, so staying up a bit later it was!
In answer to your question "How do bipolar people cope with this?" Heh. Well, I've been dealing with it for longer than you've been alive, and still, the only answer I've really managed to come up with is: Sometimes better, sometimes worse.
I'm really impressed that you've been able to do so well in regards to your BPD. I have heard that it can really be hard. Someone very dear to me has with these behaviors, coupled with no insight at all. It's painful to stand helplessly by, seeing so clearly what is happening and knowing how much pain he could save himself if he could only understand to even begin to be able to work on it. If it is ok to ask, how did you get a handle on it? How did you come to see what was going on? Did you figure it out by reading? Did someone say something? How was their approach received, and if the answer is, "not well", how would you rather they have approached it? What drove your motivation?
(Seeing how it's 6am, might be time for me to wrap it up, seeing how I've grilled you with so many questions.

Oh. Right. And sleep. Should get some of that...)