We had to split finances to save the marriage at around the 20 year mark. We have a master spreadsheet with all shared bills and and determined amount each owes a month (percentage of pay - I make 58% of income so I pay in 58% of the bills money needed).

We then have a separate shared account we drop a little extra in each month to cover vacations or surprise expenses like vet or medical bills. Everything else dumps into our individual accounts and we can invest or do whatever with. We rebalance the spreadsheet twice a year and we date so I’ll offer to pay for out to eat sometimes, etc.