If you ever lose your faith in that, then you will begin to erode your faith in yourself. Drives me nuts when I see women not let their husbands go out with the guys or are jealous of other women. I still remember back in college, it was one of my first relationships with a cute little redhead.
Overlap where you can, but not being identical should give you something to talk about and expose one another to. You will constantly feel the need to compensate and prove yourself worthy of love, which will just backfire.
A few people even said that when things start to feel stale in the relationship, they agree to have sex every day for a week. A guy who wants to have sex with you but not to take you out to dinner and a movie is not looking to have a relationship with you or even may be afraid to be seen with you in public because he is involved with someone else!!!
A good marriage makes good kids. Talk openly. Your partner will then become involved, and guess what?