Men and women tend to desire what we think we can't have. If the object of our desire is elusive - if we live in fear of losing what we want - we tend to be very persistent in our pursuit.
We want scarcity and the novelty of feeling that rush of newness and conquest to stoke our desires. The alchemy of sex has something to do with the tension between wanting, not getting and then having some of what we want. If we get it totally - then we tend to lose interest over time. If the object of our desire is not totally ours; that makes us keep up our pursuit and stimulates our hunger.
Sexual alchemy is this incredible recipe of separateness and intimacy. And here is the kicker; if we don't feel the intimacy we tend to feel unsafe in allowing the separateness.
If you are able to create a relationship where you understand and know that you have each others hearts (I have your back, you are important to me) and at the same time are able to create space - your passion can survive. It's this knowing that each person has their own lives and can never be fully owned is that is key and perhaps the only way that we can keep sexual passion alive in ongoing relationship.