Here are some reassuring words from Geoff Nicholson's Sex Collectors:
A moment's consideration suggests that a sex life consisting of never-repeated wonders would be as bizarre as it would be exasperating, to say nothing of impossible. The whole point of sex, surely, is that it's all about repetition. We know what we like, what gives us pleasure, and so we repeat those things. There'll be variations and novelties, there'll be inventiveness within the form, there'll probably be a few surprises, but the idea that every sex act might be some previously unexperienced and then unrepeatable form of escstasy is just plain silly. If it's any good, why wouldn't you want to repeat it?
It's a good point, and well worth remembering. Let's not underestimate the classics, or forget the pleasure they hold.