(WQ) The bottom line on sex is that nearly everyone is interested. It is the defining characteristic of this realm. The Kama-loka or "Sense Sphere" includes the lowest celestial worlds (beneath the Brahma worlds), the human and animal planes, and the very miserable planes.
Craving for sensual pleasures is what binds beings to this realm with its instability and attendant degrees of suffering. It is likened to a charioteer who can either control the five powerful horses of the senses or be completely at their mercy.
In order to gain liberation from Samsara, or at least from the Sense Realm (Kama-loka), it is necessary to withdraw mind and body from it completely. This withdrawal need only be temporary -- while the mind settles, concentrates, becomes blissful and bright, allowing one to successfully practice towards the gaining of liberating insight.
Thereafter, one can again indulge if one wishes: While a person has not yet attained the third stage of enlightenment (non-returning), one will still be interested in sense pleasures and sex when the mind turns to delightful sensual objects, images, and thoughts.
Given our incessant interest in this distraction and obstacle to peace and wisdom, Can there be any spiritual use for sex? Yes. For example, it can sensitize one to others and their co-development, help one gain a sense of merging and "oneness," intimacy, vulnerability, and empathy. But our society (like most societies) has so many hang ups about sex, good luck.
When sex cannot be set aside even for a few months to meditate intensively, as for example at a retreat, tantra and similar practices may be good to explore. What is the alternative -- porn, selfishness, compulsive indulgence, unresolved issues, shame, hypocrisy, and acting out? Better that one might try to transmute sensual desire into something spiritually beneficial.