At some point you will lose interest in having s*x with a woman you are seeing. The hotter the woman, the more amazing the s*x and the less frequently you see her, the longer this will take. But it’s inevitable; there are no exceptions.
And when this happens the desire to experience a new or a different woman will be much greater than the desire for your current one.
Why do you think Leonardo De Caprio looks bored most of the time despite his ability to pull more women than the average guy? Even he experiences this.