>But the two of us can’t decide the fairest way!

Because fair means different things to different people in different contexts.

And we cannot decide for you how you see your partner. Could be a traditional arrangement where in the long term one of the two earns the money and the other does the household. In that case usually, you would go for community of goods (excepting preexisting wealth, inheritance and gifts received but including new income and capital gains also on preexisting wealth)

Or could be roommates who hookup but live separate lives at the other extreme. then don't share wealth, but we cannot tell you.