sex= basic instinct of every living things in this world. Becos living thigns, live for 1 reason: to reproduce, so the species wont extinct. This is from scientific la, if got other aspect like u live becos of God, but those maybe some other religion different. So i say from scientific point. But if say sex for relationship, it is not very important. Sex is only add spice to a relationship. So, more spice, more flourish the relationship lo, but if no spice, it doesnt matter rite?