Ongoing committed relationships create obligation, which is simply not conducive to desire. But there are ways of incorporating strategies into our lives which can re-ignite desire and help reconnect. Often this has to do with unlearning previous beliefs.
We are so creative! Our minds can conceive of things that we know are taboo. But the forbidden element amps up our responses. Identifying familial and social restrictions can help us give ourselves permission to be fully and consciously expressive.
There is nothing simple about human sexuality. We are wonderfully complex beings, and often it takes time and attention to identify who we are, what we like, and who we enjoy being with. There is no "normal" - there is what you as a conscious person create.