...N-n-n-nooooo dress code. To the 10% of people who get that: you're awesome. The rest of you face the WATER CANNONS.
Right off the bat I'm going to make an inflammatory statement. I truly believe that having (some) secrets is a good thing in a relationship. No, really, I do. No. Really. I'm not talking about keeping mean-spirited secrets, or ones that may threaten your longevity as a couple but rather little, inconsequential things you omit, just for the sake of keeping the peace.
Both of you obviously have a history before one another and hopefully, when you got together you shared the ups and downs, the successes and failures of past loves. Your SO's romantic history is a road map of what brought him to you and ignoring it is like saying, "I'm happy to be American, and all...but who cares about the Civil War?" That's just silly.
BUT - and this is a big but - there's no reason to tell each other everything, like how great that last girl was in bed or how your high school boyfriend wrote you a sweeping, heartbreakingly romantic epic poem and recited it, in front of the whole school in the cafeteria one day (I'm making this up, obviously. The only poems written about me in high school were probably limericks along the lines of, "There once was a girl from Valatie / She was so, so f-ing weird.")
Certain aspects of your past and present should be just for you, and that's OK. Like your girl talk with friends or his innuendo-laden jabfest with his buddies. Quite honestly, I don't want to know what he tells his best friend. I'm sure it's descriptions of activities that kind of rhyme with, "Valatie," and, it's just not for my ears.
Above all, if someone's good at keeping his own secrets and the secrets of his friends, then he's going to be much more trustworthy with yours. That, to me, is an admirable thing. A tiny bit of mystery goes a long way.