I'm having a lot of difficulty being non reactive and not letting the words he says or his actions get to me.
This really is one of the biggest things to comitt to learning if you plan to stay in this relationship. Some things said from BPD do not really need comment, and should not be reacted to. It's different couple to couple, but while we cannot make the BPD go away, we CAN work on how our reactions to it actually fuel the fire and make things even worse.
I look at it a lot like my H has a disability. Instead of being in a chair or having some obvious visible sign he has it, it's tied to his emotions. Much like a condition like diabetes, with proper care, mindfulness and a change in behaviors, it can be easier to live with, but there will still be bad days or the potential for things to get off track.
Looking at it like this helps me, a little, not focus as much on how much some comments sting, hurt, are meant to be mean, are just plain wrong, and often are intended to trigger me into fighting so he can vent his painfully negative emotions.
He has confided, after many years, that he cannot feel he got his anger out unless he yells at a person. This was a big breakthrough for us. So he's mad at the weather - has to yell at me. Has a flat tire? Has to yell at me. Mad at his boss, you get the idea. Knowing this, even though I know it's not right for him to yell at me when I'm not the cause of things (and he HAS overall gotten better even if right now he's struggling) has helped me distance myself a bit from allowing the hurt in.
pwBPD can't admit their own culpability in their own drama, and so they pick fights to be free to turn it around and blame YOU for the fight THEY started. In their head, it all makes sense. They'd not need to fight with you if you;d just not do things they think make them upset (even if they were already used before you even came into the room).
That's one of my big boundaries - a barrier around the hurt I could allow myself to feel if I did not realize that BPD is a bit like alcohol - it may make you say things that make sense at the time and "feel" like they are true, but they aren't. So when he goes off, I distance myself physically if possible, and emotionally regardless. I see the BPD as an emotional parasite, feeding off of his inability to control himself at times. Like the witch in Hansel and Gretel fattening them up with sweets, BPD wants to feast on dysfunction and anger and rage.
H has similar ups and downs - he's either the best whatever in the world, damn everyone else, or he's pond scum, the lowest of the low. Neither is good, as they are both exaggerations and extremes, as one type of thinking set up the other a few days later when it all falls apart.
Yes - it's hurtful. And it sucks - as the more emotionally "able" person, YOU will bear a larger brunt of the responsibility for managing your own actions than your SO will his. YOU will be more mindful, and likely in some cases more of an adult at times. That is part of accepting staying and working on it - you accept that your loved one is disabled, just in a way that is hard to see unless you are around 24/7. Therapy, IMO, is shakey at best for BPD - they often can't take the advice of a therapist as it is probably quite invalidating. Posting here helps. Writing helps. Reading the tools and lessons help.