PwPBP must learn to self-soothe. It does nobody, including the pwBPD, any good to rant and rave and lash out at others. Sure, they will feel better after they have discharged their anger, but it is very destructive to the relationship and is bad habit that should not be reinforced.
The best thing to do is to disengage from the conversation in a calm, sympathetic manner, by saying something like, “Hey babe, I’m sorry that you’re upset but I’m not willing to listen any longer. I’m going to go out for a walk/into the other room for 20 minutes and then I’ll be back.” Then you come back and if they start ranting again, you rinse and repeat. Eventually they will learn that acting out = disconnection and learn to reign in their anger.
As far as why you ended up marrying a pwBPD, perhaps this piece about the repetition compulsion will help answer that question:
https://seattlecommunitycare.com/freuds-masterpiece-the-repetition-compulsion/