I think sex itself is not as important as people tend to make it.
you can have sex with a number of random strangers and it can mean nothing and is forgotten as quick as it happened sometimes,however,having a sensual,maybe sexual,experience where you feel truly happy with the person your with and truly connected with that person is extremely important in a relationship imo.
that experience doesnt have to be sex,it could be a nice massage or just cuddling up having a chat but whats important is that at that moment your truly happy and loving the fact your with that person.......................................................................all that said id pass out if i didnt have a wild, rampant,no holes barred sex session at least once a month!!!!!