My partner and I, though not married, have a joint account where each of us designates a monthly amount from our separate accounts, to use for expenses and fun stuff we do together like a movie, dinner, or a trip. We are in our 30s though and have a solid relationship. Probably in my 20s, I would have been reluctant to make a joint account too. But besides all, I agree, separate accounts should stay and, in our case, we both decided to keep them since it's important to just feel financially secure and free to do anything you want or need with the money you earned.

So, OP, NTA, I think you have the right to decide what you do with what you've earned and also how exposed you want to become. His reaction is also unreasonable because you already share costs, it's not like you don't contribute. My grandma taught me I should always make sure to have my own money, as you never know. She may have been old-fashioned and gone through many hardships, but overall not bad advice.