Mara is mostly right although i don't believe that "cure" is a good word to use with BP since I don't believe anyone is ever cured of it. Since it's a brain issue, the medicines can many times get rid of the symptoms for the most part but being cured would imply that the meds would at one point no longer be needed.

Besides the distinction of causal differences between bpd and bp, the other thing would be the traits. Although they can overlap, there are distinct differences, where although bpd has emotional dysregulation surfacing in the form of mood swings, the bp will have these mood swings based on the brain alone whereas the bpd usually has a trigger that causes a mood swing, even though many times it "seems" as though it just "happened". I know that when I'm really analyzing my emotions, I can almost always find something that caused the swing. Most times the negative mood shifts are caused by fears. That's my experience anyway.

Read up on bpd. It's detailed enough that if you do that you'll probably know one way or the other whether it's bp or bpd.