Sex and sexuality is about more than just two people, a bed, and a few aphrodisiacs. Scientists study why humans have sexual intercourse (it is good for you and good for the species) and how sex is driven by evolution, genes, emotions and more. There is also much to learn about the differing roles of men and women in the whole mating game. Yes, there's lots of science to explore. Not that an aphrodisiac isn't more fun.
A 'brightly fluorescent protein' has been revealed in some species of marine eels causing them to glow. Researchers have speculated that, because the full moon 'excites' the glow of the sea creature, this may be a mating adaptation.
Aliens might have sex, assuming the benefits outweigh the risks on their home planets. What that sex would look like is an open question. But if animal antics on Earth say anything, extraterrestrial sex would be weird.