Hi there,
I understand your pain. My ex partner of a year who I was very much in love with suddenly had a first episode of psychosis last year, seemingly out of the blue (although I can look back now and see warning signs but it would have been impossible to predict regardless) and it still haunts me today. We had a seemingly healthy relationship - never fought, discussed things calmly, mostly just laughed and enjoyed each other's company and it was starting to feel really serious with a lot of long term potential. He expressed wanting to live together soon and then soon after became manic and eventually hospitalised for psychosis. Thankfully, with medication he stopped having psychotic symptoms quickly but recovery is a long road and he wasn't quite the same after - it may be some time until your partner is back to full health again.
As you've mentioned, this is particularly difficult because it feels isolating. I don't know anyone else whose partner experienced psychosis (or it's just not something people share so I wouldn't know even if that was the case) so it's hard for my family and friends to relate when I've sought their support. It's not something people are comfortable talking about and the privacy of the partner is also important so it's also hard not being able to talk to everyone about the psychosis. I just say 'my ex partner was struggling with mental health'.
What helped me during his recovery phase, because I intended to stick by him after his episode, was exercise. I took up running and did yoga sometimes. I also booked myself in straight away to a psychologist to handle this experience which I'd recommend. However, even with good self-care it was still the most emotionally traumatising thing I've ever experienced - and still is, as I try to undertand what happened and what to believe. That's the hardest part. e.g. do I believe his wish to live together and that he loves me and has never trusted anyone as much as me, or his poor treatment of me and lack of care he expressed before the break up? Do I believe the beautiful or the horrible things he said to me while psychotic? What was true? What was him and what was his illness? He told me horrible things during the episode like 'I didn't mean it the first time I said I loved you' 'I think I need to leave this relationship' and he accused me of not trusting him because I wouldn't get drugs from a doctor to give to him. But then he'd call me the love of his life and say I had a heart of gold. I got through it by dividing his personality into 2 people - the psychotic stranger and the man I loved. But it was very hard as the line between the 2 became blurred during his recovery when some themes during his psychosis bubbled to the surface again while he was on medication.
He actually broke up with me 4 months after his episode (citing possible relationship OCD, nagging doubts we're not right for each other for shallow reasons, and the fact he was unwell which I fully respected/accepted because he wasn't emotionally stable enough to be in a relationship at that time and it was starting to give me panic attacks and anxiety at night). It's important to ask yourself if you're better together or apart during this time, as soul-crushing as I know that question is. Please put your mental health first and acknowledge your needs and, once your partner stops having psychotic symptoms, communicate a lot! Ask the difficult questions and share your needs while still acknowledging his needs. I put my ex's needs before mine and could have avoided prolonged anxiety and stress if I'd pushed him to be more honest with me about what he needed - which was to be alone with his family right now.
I think what has helped me the most is telling myself: "there's nothing for me to do now - I can be a good partner but I'm not responsible for his mental health, I'm not qualified to handle an illness like this so I should forgive myself for not handling things 'perfectly', it's not my job to understand what's happening in his mind and I don't need to stress myself out trying to unpack or solve what's going on because it's impossible". Know that you can only do so much. It brings some relief to practice acceptance of the fact that you won't fully understand what is happening, why it's happening, or what you can do. But neither did my partner, he was just as confused - I do still feel a lot of empathy and love for him and really hope he's ok. You can offer support, be loving, but ultimately this is a situation that you have limited control over sadly. And also remember - mental illness is no excuse for treating a partner badly or with a lack of care or love, even though this is a special circumstance and some allowances will need to be made.
Take care and I hope your partner recovers quickly and feels better soon.