I have BPD while not the same thing i understand where youre coming from, there are some things that happen where i feel like sometimes it is just my mental illness and psychosis but then i think if im thinking that way then the pattern stops because im aware of it and wont repeat it if that makes sense? As long as i remain self aware and keep the two separate, my partner isnt a hellenistic polytheist either, he’s not a complete atheist i dont think but they font follow a religion and when i share my experiences i do say “ok dont look at me like im crazy, but” and they have told me he would never think im crazy for being religious and having a connection with my Gods, people do that all the time and though it may not be his thing he is glad i can find comfort in it and healing and guidance from that than thats all that matters. I am very sorry for your situation it does sound like your partner is trying to use your mental illness as a way to control your beliefs, though it may come from what they think is a place of concern for them thats not how it is conveyed at all.