To be honest, I'm more concerned about your usage of they when talking about your partner. In my circle that indicates transgender which is a significant cost by it's own. I'd say, you need clarity on what expenses are expected from you in the future.
Ok. Because this topic just won't die. We're lesbians.
I used they not only for privacy reasons but because it isn't relevant to the discussion. I'm going to assume best intentions but this was a pretty weird comment. Are you actually concerned with my SO's future healthcare spending? Do you talk to people with diabetes or MS the way you talk about trans people here?
My dad is gay, my wife's uncle had MS (he died), two acquaintances have MS and one has diabetes, a person that inspired me was transgender, although she unfortunately died last year. I work in healthcare, so have some ideas of the financial impact, which is the only thing I mentioned... without judgement, BTW. I also live in a different part of the world, I presume, where other social norms apply, and my remark wouldn't have seen as too inappropriate. I don't speak English as a native language. I do appreciate that you are assuming best intentions, unlike some other's here, that seem to assume that everyone has a US background, when I'm neither hiding age nor locaton in this forum.
Now that this is hopefully out of the way...
I understand that people can be cautious about talking about finances as it's been often treated as sensitive information one doesn't share. At this point I would understand if they haven't shared all details with you, but I also would see moving in as a time where it would be appropriate to ask for more details. They might not want to share everything pro-actively because they never have been tought to share this kind of information, but they definitely should share when you ask - after some time to make up their mind, of course.
Starting a business is an adventure full of uncertainties. All they have is hope that it works out and they make money. I obviously can't speak about your partner, but when I started my business, my perspective on this changed daily, if not more frequently. It took me many years before my mood did not change on any prospect client, on any lost contract, on any paid invoice, on any tax payment I had to make. It's a rollercoaster... Even today after more than 20 years I would hesitate to make a clear statement regarding future finances, and I know my wife since I was 13 and finances is one of my focuses.
My wife wasn't certainly happy all the time, but she trusted me and my plan for which I'm forever grateful. I imagine it must have been similarly difficult for her and it took quite some time before it looked positive to her which was years after it looked great to me.