Rather than Jim's multiple moving parts, I like to keep things simple and transparent. We're both on each other's accounts, and have all the passwords, etc. The transparency eliminates curiosity and suspicion.
SO and I agree to a "fun money" allowance for each of us per paycheck for the coming year when we do our taxes, & plan for major expenditures (home renovations, vacations, vehicles, etc.). Each month when we sit down and pay all the bills, we also deposit savings for the expenditures, and split the fun money amount. She spends hers on Amazon Prime, Starbucks and Yoga classes. You all can guess where I spend mine, but she thinks its the occasional happy hour,, night out with my buddies, and Quizzo.
She knows what I'm spending, and I know what she's spending. If we have financial needs that eliminate the fun money temporarily (since life happens), we both go without, and I need to man up and stop mongering until fun money is available again.
Again, the above is what works for us. For many, money discussions are equal to a power struggle. My SO saw it the same way initially, too, but eventually she realized she has as much agency over our money has I do.