So sorry to hear about what your husband (and you) are going through. BPD is difficult to treat, and health care systems with limited resources often push them away because they are not easy fixes. Or worse, misdiagnose them with depression/anxiety/autism/ADHD and just try to paper things over with meds and shrugs about things being permanent.
You say he is in episodes 90% of the time, what are those episodes like? I am also curious what therapies he has been through and what other options you have. NHS, that's in the UK, right? I'm in the US and not familiar with resources in the NHS--are you able to send him to hospital if he is suicidal? Are there private practice therapists or psychiatrists?
Have you purchased or read any books on Borderline Personality Disorder? There are both books for family members of those with BPD (like Stop Walking on Eggshells) and books for people with BPD. For example, anyone can purchase Dr. Linehan's DBT skills workbook and training manual.
And I feel awful that I'm losing patience...not love, not empathy, but my patience is being tested and I feel so guilty about it.
It was actually Chat GPT that directed me here, which sounds so depressing haha, that my biggest support is coming from an AI app...
I think all of us on this website have found our patience being tested (or totally exhausted). One of the quotes from Stop Walking on Eggshells is a person stating that making their partner with BPD feel loved is like trying to fill the Grand Canyon with a squirt gun, but with one difference, the Grand Canyon has a bottom. I have felt that way countless of times. I have found I can't do everything for my wife. There's actually little I can do to change her even if I feel a lot of love (or guilt). I can only be supportive.
It kind of makes me relate to all our ancestors who had to deal with sick family members before modern medicine was invented. They just gave them water, wiped their foreheads, and hoped the person pulled through.
I largely don't confide in anyone because I don't want anyone to judge him or think of him differently.
I think you hit the nail on the head there. It's really hard to carry these burdens alone. I tried and started to have suicidal thoughts myself, so I reached out for help. My wife still hasn't forgiven me for that... but I have because I know I needed it.