Re becoming your own person, it sounds like you've already done the hard part and acknowledged some really difficult stuff. None of us know you irl but I think we're all quite proud of you!
I'd say the next step is to try and combat all the isolation you're experiencing. It will help you get perspective on things. Can you join any local home education networks or groups? Is there a local library you can join, or classes? I think you need friends where you are and possibly back home too. Can you reach out to anyone through Facebook?
Do you think you could get him to go to couple's counselling? Maybe you'd both benefit from time with a third party who can help you to see a fairer financial system? That also may help with the OW issue.
As for when/why you care about money: you have given up your own earning potential for years to raise your DC. You have every right to know how we plans to support you and DC in everything you need. Does he have enough to cover their tuition for university, for example? Though tbh, this comment had me thinking ltb, he's not being honest with you and never has been.
And if your property is in both your names, half the proceeds from renting it out belong to you. And you should know any and all house repairs that are being funded by his family, and on what terms. Is that money a gift? A loan? Does he make repayments to them? Are you paying the right amounts of tax on that income?
I suspect the reason he doesn't tell you any of this, or explain his family money situation, is because he's trying to protect it. This is also probably the reason you aren't already married.
I'm intrigued by his family setup though. I know a lot of boarding school background people, I work at a very established independent school and speak to families like this every day. I think every single person I've ever met from this background would be mortified at the thought of their sahm having to cut their own hair/not having money to participate in things. Unless his mother cuts her own hair (in which case they are barking mad and will never change) you're being mislead somewhere.