For what it's worth, my wife and I have a budgeting system that has worked out really well. We have 3 checking accounts:
1) Joint Account
2) My 'Fun' Account
3) Her 'Fun' Account
Our respective paychecks both dump into the Joint Account where we pay the bills, groceries, trips, outings both of us attend -- essentially the bulk of our spending and anything we both agree on. Then we each get a certain amount automatically transferred to our respective Fun accounts each month. The rule being that you cannot question what the other person spends their fun money on at all. I spend mine mainly on brewing and going out w/ the guys. She spends hers on girl time and purses/shoes.
Since she drinks some of my homebrew, I get to brew one 5 gallon batch a month on the joint account as well -- but all the equipment and any excess brewing comes out of my fun account.
This system has worked great for us both, we NEVER have financial arguments and we both get to do what we want, within reason. I'd highly recommend it to this scenario.
Regardless, good luck!