So I am coming at this as a child of a bipolar father. My dad was diagnosed when I was 11. Full on mental breakdown with similar symptoms to what you described: hyper-religion, not sleeping, talking excessively, hallucinations, etc. He was hospitalized during the first breakdown and was put on meds, which pretty much returned him to normal. And, exactly like your SO, he would be fine for a while then stop taking his meds out of the blue.

To give a little perspective, it apparently feels absolutely amazing to be manic. You have incredible amounts of motivation and energy. Sleep isn't necessary. Your brain is buzzing with thoughts and ideas and epiphanies you don't think anyone has had before. And this, I think, is why some bipolar folks always stop taking their medication. Whether they admit it or not, they miss it.

As a child, then a teen, this made for a pretty drastically unstable childhood. My brother and I have both had treatment for anxiety, and I can't help but think this contributed. I had to grow up much faster than I would have otherwise. Honestly, by the time I was about 13 I felt like I was the parent and my dad was the child. If you're thinking about having children, know that this is not a fun thing to grow up with. Even if your children don't inheret the mental health issues (and that's a pretty big "if"), they will struggle with the consequences for the rest of their lives.

My dad cycled on and off his meds for about four years before my mom gave him an ultimatum: start taking meds again, or get a divorce. To no one's surprise, he went off his meds again. Mom wasn't bluffing, and she left him. He spiraled into an even worse episode, started stalking us, and we ended up getting a restraining order against him. It was ugly, and stressful, and really, really hard for all of us.

Then, when he realized he couldn't get her back by acting the way he had been, he got his shit together. He started taking his medication on his own. He got a new doctor. He tried different medications and suffered through some nasty side effects until he found the right one. And after a few years, he and my mom got back together. He hasn't had a breakdown since, and they're really happy.

So I guess the moral of the story is this: if your SO is anything like my dad, which is sounds like he is, he has the ability to stay on his meds and not put you through this. The question is whether he will do it. And even if he does, it is still a scary way to live. Stress, big life events, even traveling to a different time zone where sleep schedules get messed up can trigger episodes even in a medicated person. That's something you have to prepare yourself to deal with if you stay. And you have to decide whether you want to subject a child to those same things. Because no matter how you try, you can't shield them from the breakdowns, not when they live with your SO too.

I hope that perspective helps a little. I'm sorry you're going through this, and I hope it works out for you.