Bipolar and borderline are very similar, but borderline is more about personal relationships with others, and bipolar is more about your own sense of self-worth.

Bipolar people will fluctuate between mania (extremely high sense of empowerment) and depression (speaks for itself), i.e. manic-depression. Borderline people typically are just depressed and heavily dependent on other people, and will react extremely to positives and negatives shown to them. (Very reliant on affection, will assume the worst if not shown any.)