Research indicates that there are all kinds of secrets partners keep from each other, and while some are less-than-ideal (cheating, debt, and drug use), many are completely innocuous. For example, a recent study done at Columbia University found that many people keep lofty career or personal aspirations to themselves. In this case, the secrecy isn't personal, it's just that they're not prepared to talk about it yet, probably because they're still working it out in their own mind-and that's 100 percent okay.

It's one thing for your S.O. or spouse to keep their student debt or sky-high credit card bills from you, but it's totally another if you're in a good financial situation and they have a little extra cash stashed away for their own personal use. "Everyone should have a 'rainy day' savings that will cover them in case of emergency," says Karolina Pasko, psychotherapist and coach. "It's untouchable and locked. No one needs to know about it." Including you.

3. What Their Ex Was Really Like

You've probably had at least a cursory conversation about your partner's past relationships-but you might not have the whole story about each and every one of them, and it's better that way. "One of the biggest client secrets I've found is past relationship history," says Rosalind Sedacca, dating and relationship coach. "We may have regrets about how we treated a partner. These secrets are sometimes better left untold."

If your partner learned their lesson about what they did or what they shouldn't put up with, there's no reason they should have to tell you about it. Of course, if they're still feeling the emotional impact of their cheating ex and it's causing them to act jealous or suspicious, that's a different story. And remember: still feeling hung up on past mistakes and relationships is one of the signs a person should be single.