In R-rated movies and novels sex is a major theme, but it's never marital sex. "Hot sex" is either with a new partner or an extra-marital affair. The meta-message is the best sex is spontaneous, dramatic, both people are turned-on before touching begins, and sex always culminates in intercourse and orgasm. Is this the right model for couples in marital or serious relationships? Clearly, the answer is no.
The real question is whether couples can maintain sexual desire in a relationship that lasts 10, 20, or even 50 years. The book "Enduring Desire" presents strategies and techniques that facilitate developing and maintaining a strong, resilient satisfying couple sexual desire.
Sexual desire is the core dimension of healthy couple sexuality. You cannot treat sexuality, especially desire, with benign neglect. The psychobiosocial model of couple sexuality promotes psychological, biological, relational, and psychosexual skill factors which enhance sexual desire and function. The core psychological factors are accepting the challenge to enhance sexual desire, positive anticipation of touching and sexuality, and feeling you deserve sexual pleasure at 30, 50, and 80. Biologically, what is good for your physical body is good for your sexuality--so maintaining health behavioral habits of sleep, exercise, eating, not smoking, and not misusing alcohol or drugs is crucial. When dealing with illness and sexual side-effects of medications, a prime strategy is to consult as a couple with your internist or specialist to reinforce being an active patient and explore how to reduce unwanted sexual side-effects (or compensate for them).