5. Lying About Money
We've all been there: We spent far too much on something, then lied to our partner and said it was on sale. 

How to break it: While your money is your money is one thing, if you're sharing a bank account, that's a whole other ballpark. The best way to break this bad habit is not to do it. I realize it's easier said than done, but seriously: just don't do it. If you're planning to start a life together, you want to be honest and upfront about money from the beginning.