Hi! Welcome, you'll certainly find a lot of helpful information here.
One of the things that struck me right away is you've been with this person just a few months and and living together now so this is a new relationship for you?
I've been with with someone who has had these issues for 25 years. My wife is uBPD and started out very mild in the beginning, at first I just thought it was maybe bad PMS/PMDD. It took me until just this the last year before I found out what BPD was and that my wife has it.
It's been extremely challenging and both myself and the kids have been subjected to varying levels of abuse as it's gotten worse over the past 6-8 years: emotional, verbal, and even some physical towards me
It's a very exhausting road and if I knew 25 years ago about this disorder and it's impact I don't know if I would have entered into this relationship. It's been very damaging to me, I'm working on a lot of things but I have a long road ahead. It's hard to know which way is up and figure out what boundaries I need to setup. It's been so damaging to our kids as well.
All this said I think you should continue to look here and do some research. I would recommend a couple of books to start:
Stop caretaking the borderline or narcissist
Stop walking on eggshells
I know for my situation I've come to the full acceptance that I'm married to a mentally ill person and she may never get better/change. The ONLY thing I can do is figure out what sort of boundaries I can establish to try to create a life for myself, and stick to them. But it's hard to impossible to imagine ever living a normal life. Even though I've been reading books and her for 6 months I've barely made a step in setting any sort of boundaries. I feel even though I know what's happening and trying to stop being a caretaker I still end up doing it.
If you're this early in your relationship and it's already this volatile you have to ask yourself if this is the person you want to be in a relationship long term/forever? And if you're so accepting of this sort of behavior especially this early then you might be like a lot of us non-BPD partners - with codependent / caretaking tendencies. Most people would run at the first sign of this sort of behavior but not us caretakers

I wish I would have gotten in therapy a LONG time ago, maybe you want to find yourself a therapist?
Do your research and read - good luck friend.