Honesty 99% of the time is the best policy with relationships. Are you lying if you're just selective about what you share? According to one relationship expert, it's a myth that you should divulge every detail to your partner. Really? Hmm this should be interesting.

Marti Olsen Laney, co-author of The Introvert and Extrovert in Love says, "Even though you're part of a twosome, your relationship will thrive if you maintain a private side." Plus, she adds, some things might hurt your partner, so keeping quiet will prevent needless stress on your bond."

Here's are the five most important things from Cosmo to keep from your guy:

1) Past relationships: Men may ask about other guys, but what he really wants to hear is he's the best.

2) How much money you spent on that dress: It stresses guys out to see you buy things they deem unimportant (like clothes or shoes). If he compliments your dress, just say thanks and leave it at that.

3) The way you feel about his family: The minute you say something negative about his family, he will feel like you're making him choose between them and you, and he'll resent you for it. I watched friends end relationships on this problem.

4) Innocent flirtations: It may be tempting to brag that you still get male attention, but it'll just make him feel insecure. Keep quiet and take pleasure in the fact that you've still got it going on.

5) What you really think of his gift: Men aren't super expressive, so a gift is their way of saying they care. If you reject it, you reject him.

What do you keep or think should be kept from your guy?