A lot of men of his generation - and mine - inherited their own father's approach to money - he was the breadwinner, gave his wife housekeeping, and she didn;t need to bother her little head with the details.
I think if you both work and contribute, there should be a l\arger degree of mutual openess than seems to be going on here.
I supported my girlfriend - now wife, through college, and we were poor as church mice. She went from being a barmaid to teacher, Deputy Head, head, and now ISI and OFSTED Schools Inspector, so for the majority of our time, she heas earned more than me. We have separate accounts - always have, but no secrets, and money is freely discussed and shared.
If she - or indeed I - suddenly became secretive about our finances, I think the other would wonder what is to hide, and more importantly, why?
I think you need to have a chat with him. Ask him why the sudden change in his attitude, and if he tells you it's not your business, remind him that it very much is, and you want to clear the air. If he gets stroppy, he's hiding something, and you need to pursue it. Nothing will be solved by ignoring the situation.
It may be something innocent, but it may not - and you need to know which it is, and now.