[Lucid:]

I know you don't share a bank account, but there are ways to still keep track of all of his and your money. I personally like to use mint.com. It syncs with your bank account(s) to keep a list of all your purchases, it's got budgeting tools that yell at you if you go over budget, and it tells you what categories of purchases you spend all your money on. You can hook up both your bank accounts to one profile so you both can be completely open with each other about where your money is going. If you don't want to use the site, a similar option is just to ask to look at his bank statement - but if you share a mint account you can both check on the money at any time you want. If you're essentially sharing money anyway, he should agree to let you see where he's spending it unless there's something sketchy going on that he doesn't want you to know about. And if it's just a matter of not watching where all the money is going, knowing that's the issue will help you both prioritize your budget in the future.

Also if you have $400 you have enough to go buy a week's worth of food... =/