We have all heard stories about joint bank statements ruining relationships. It's hard to explain that $1000 bill from Cartier if your girl's wrist is ice-free. Now that there are so many ways to manage your money, there are new ways for your wallet to come back to haunt you. Useful apps like Mint will send you alerts that say things like, "You have spent $500 on restaurants this month." If your girl sees that while you're both at the crib eating Papa Johns and watching Duck Dynasty, things might get ugly fast.