I tried for a while telling my gf I suspected she had BPD, she would brush it off and forget about it every time.
I kept learning and started using the tools, things got a lot better, she even said "whatever you're doing is working", so she did notice the change even if she wouldn't acknowledge the problem "I was working on".
Look at it on your own end, how have you changed based on her responses? most people say they do one thing or another not to trigger their partners, it is my experience that people with BPD are also affected by our own behaviors and limits, just the reaction might not be as you expected, as in, they might brush it off but be more careful not to step on your proverbial toes next time.
Its not about "do it because its good for you", there need to be things you will not engage with and others you will reward. there will be things outside your control and you also have to be aware of that, so don't pressure yourself if things go bad every once in a while (my gf cut me off after I had been busy/distant for a few days, haven't heard from her in a month now haha), even the best couples have their ups and downs.
I feel like unless she agrees to address this we are doomed.
Reality is more of a rainbow of possibilities rather than a monochrome black and white, perfect or doom. Try to see the mixed colors of good and bad and annoyingly charming with a touch of background vulnerability in your interactions, might change your perspective on things.
And keep posting! there's good people here that try their best to help, at the very least having someone that will listen can lift some weight off your shoulders, it sure did for me.
