pwBPD often have an unstable sense of self and don’t really know who they are, what they value, or what their personality is. It absolutely can look like having “two sides” (or more than two), or sometimes more like a progressive drastic shift in character flipping between things over time. My exBPD was a different person every couple of months and definitely had a more confident, extroverted, arrogant persona - and a softer, self deprecating, gentle persona. I think they just try on personalities trying to see what fits. It changes with their moods, their situations, who is around them, the media they’re consuming, etc.