Nicholas Monserrat, famous British author of "The Cruel Sea," once wrote a book called, "Depends What You Mean by Love." In it, different types of love were depicted. But here's my opinion.
Sex is an inherent urge of body and mind: love is impelled by the spirit. When all three are involved then the sex is, as mentioned by several othes Hubbers, something indescribably wonderful. But if a lover (loved one) in the real sense is not available, sexual release is still desirable on a fairly regular basis, subject to one's natural libido. If unconditional love were essential before people could enjoy a good nookie, there'd be no call for prostitutes and brothels. Also, the fun would be taken out of the chase, which so many indulge in to find a sexual partner. Most men 'hit the town' to find a sexual partner, not to find a true-love life partner - leastways, that's the way it seems to be.