There is not one person who can fulfill all your needs. You may choose a partner who is your intellectual equal, and he may not be your most compatible sexual partner. And then there's the duality between security and adventure. A relationship that gives you plenty of novelty, and adventure, may not provide the stability you long for. Time, continuity and familiarity with somebody gives you other things in life but won't necessarily give you the kind of intense lustful experiences that you may have when you first meet someone and are curious about penetrating the mystery of them.