I have been living with my bipolar DP for 7 years, but we only really found out a couple of years ago what was wrong after a major mixed episode.
Your partners behaviour sounds very similar to my how my DP was during the buildup to it. It started with her getting more irritable than usual. Minor things that normally wouldn't have bothered her worse suddenly major issues, and she refused to belive that I could possibly have any issues with her and every problem was my fault. And yes, what you describe as "BPD" like behaviour was certainly part of it. IT doesn't mean he has BPD, it's just part of the psychosis he is experiencing. They seem to be able to convincingly argue that black is white, and you really aren't sure whether it really is black even though it's in front of you. Anyway, it kept getting worse and worse until I was convinced that whatever I did, our relationship would soon be over. I figured it must have been me. Perhaps I really was that impossible to live with.
But when it reached its peak, I realised it wasn't right. Her behaviour was completely out of charactor for her, the things she was saying were things I knew she woudln'r normally have believed, and she was just too erratic and to be OK.
I had already realised that arguing with her was a waste of time. It just escalated until she was ordering me out of the house, when truth be told I had no idea what we even arguing about. I tried remaining calm (Vulcan-like calm, not just your regular calm) and this seemed to help. Trying to remind her of how much me and the kids loved her just seemed to make her feel more claustrophobic. So I just gave her space. It seemed the best thing to do. The agreession seemed to subside a little.
I also tried to suggest she seak some help, but this resulting and screaming and shouting about attempting to lubotomise her. So I had to just wait and pick up the pieces afterwards. Once she was back to normal, she was so ashamed of her behaviour that she expected me to leave. She thought no one could or should put up with her. But, to be honest, whilst we've had other minor episodes, this was the only one in 7 years that was truly distructive and extremely difficult. I decided that I loved her enough to put up with 3-4 months of this. And she was quite willing to accept treatment once she was normal again.
Regarding advice to leave your partner and run for the hills. Well, obviously I didn't follow that. But have no preconceptions, its not easy. It will require work and patience on your part, and a willingness to try from him when he is his normal state of mind. This is a crossroads for you, as well. Do you love this person enough to make a commitment to stand by them through these very trying epsiodes? Can you support them when they're down, give them space when they're up and help pick up the pieces when they come down? For me, it was yes. But only you really know what the answer is for you.
The episode he is in right now is not the man you know and love, remember that. His mind is such a swirling mess of madness that he barely knows what he's thinking or feeling. Give him space, and judge him on when he is in his normal state. Not on how he behaves right now. It's easy to make things worse. But with effort, keeping extremely calm around him and not forcing him to deal with your feelings right now is what is going to help.
If you have some support, use it. Talk to a friend or family member you can rely on for support. And when he comes back from this episode, when he is ready (because he'll be in shut-down mode for a while) then he'll want to talk to you about your feelings.