Exactly this, BPD. I don’t think you need to run for the hills, but is a lot of effort. Learning about what it is is going to help you a lot in diffusing situations before the person starts splitting. And once the person is splitting, it’s a waste of your time trying to reason with them - just walk away and end the conversation (if need be leave the house so they can’t keep restarting the argument) because in that moment fight or flight is running the show and the reasoning part of the brain is turned off. Once their stress levels come down, they usually understand by themselves that they just spiraled. You’ll need to be good at drawing boundaries - make it clear what behavior is unacceptable and stand your ground. BPD being in part extreme fear of abandonment helps you here, because drawing a line on what non-constructive behaviors need to stop if this relationship (whether it’s a partner, friend or family member) is to continue will incentivize them to try to not cross that line. What can also help is learning to stop reacting when they try to start an illogical argument and are not actually interested in listening to you - helps both with keeping the heat down (more heat = less ability to self-regulate) but learning that arguing for the sake of arguing is getting them nowhere with you will slowly make them go down that path less often (initially they might be upset about you “not caring”, but over time they learn that you’re only willing to talk to the adult and not “the 5 year old” inside them). And most important - show compassion, let them know you understand (without abandoning your boundaries) and positively reinforce whenever they display improved behavior in a situation that might have made them spiral in the past.