> All untreated BPDs experience splitting. For me, that isn't up for debate

I don't know where you got that information from, but I'll assume it's the bad experiences you mentioned. I'm sorry you made them. "a pattern of unstable and intense interpersonal relationships characterized by alternating between extremes of idealization and devaluation" is one of nine criterias used to diagnose BPD. One must fulfil only five, however. Please try not to make those generalizations. It's important. People suffering from borderline are still individual humans. Even if they have similar (not the same) problems as the ones who hurt you, it's not fair to divert your disappointment.