I had this problem with my significant other. The solution was simple:

3 different bank accounts.

1. We each put 75% of our income into the family account. Bills, family expenses, and family outings come out of it.
2. I put 25% of my income into my personal account. They don’t get to see it.
3. They put 25% of their income into their personal account. I don’t get to see it.

Ratio has occasionally been adjusted based on living expenses vs combined income. (All the way from 90%-10% to 50%-50%). And we’ve never had a money argument since.