Ive had disagreements with people over whether or not most people ever achieve long lasting complete sexual fulfilment.

In short, I don't think people do. They might have some short lived sexual satisfaction, but ultimately they get dissatisfied again at some point, or their satisfaction was always less than total.

I think most people live lives of quiet desperation and this sexually, as well as other areas.

Indeed, I go so far as to say that for most people complete sexual fulfillment is impossible because they desire unrealistic or contradictory things. That human sexuality is doomed to render one always unsatisfied to at least some degree.