In my experience, it's impossible to be just friends after a romantic relationship... .I don't really want to hear about how she got drunk and had intense, intimate relationships with a bunch of different guys... .
These things are easily mitigated, in a friendship situation, by defining and maintaining boundaries that are healthy for you. If you don't want to hear about her getting drunk and being intimate with others, don't allow the conversation.
By defining and maintaining boundaries, we are in control of what we allow into our lives. I have many friends from whom I don't want to hear stories about their drunken, sexual exploits. I just leave the conversation or change the subject. The same applies with a pwBPD. It's just like any other friendship.