Money is a dicey issue, and whether you're just "withholding" information about a small purchase or lying about the amount of debt, deceiving your partner can hurt the relationship.
Insecurities about your money situation might be holding you back from the money talk, but there are smoother ways of introducing the topic. For example, couples can take advantage of tax season to bring up money questions that they were holding back. My suggestion for other times to do it is the year-end bonus period, when either one of you is checking your credit score, making a major purchase, or paying bills. Another way of casually introducing the money topic is to talk about a finance article that pertains to your question. Remember, there's nothing wrong about talking frankly about serious issues with your partner, so don't be afraid to bring it up even without these conversation starters!