It is completely possible you *just* have BPD. From following your threads on the Bipolar board, I have personally thought that for a while.

If you can get the BPD under control your life will have more meaning, less boredom and you will have more appreciation for the good things. Have you ever done a DBT program? You might find it very useful.

There are a whole lot of BPD's wrongly diagnosed with Bipolar, it seems to be far more common in the US for there to be a BPD and BP diagnosis than a straight diagnosis one way or the other. While it is possible to have both, it is not as common as it is diagnosed. Usually the patient does just have BPD and once that is properly treated and under control they no longer have any "bipolar" episodes.