Laura, I really sympathize – I’ve been in a relationship with similar dynamics. In my case, my partner was very knowledgeable and authoritative in most aspects of his life; he was usually the smartest person in the room and used to being in charge. Professionally that worked fine, but when it came to handling household finances, he didn’t always seem to “hear” my input. To me it felt like we weren’t making joint decisions. It made me feel frustrated and anxious.
I agree with Carla that a trusted third person joining or mediating the conversation might be the answer. In my case it was a mutual friend (an attorney) with solid financial background. Having the friend “moderate” defused the conversation and made it more about the numbers, less about the personal dynamics, if that makes sense?