[Mithalwen]

If I can phrase this delicately, LACE makes it clear that while elves have sex soley within the context of marriage it was to them not merely a necessity to the production of children but a great pleasure.

Since consummation was integral to the validity of a marriage and there was usually a significant gap between the marriage and first childbirth and long spaces between children I think it is reasonable to assume that it was a recreational as well as procreational activity.

LACE also states that elves put more of their own strength into their children which is a reason for their having few children. Also that the elvish body was subject to the will which implies that elves could contol their fertility by mind over matter - lucky things! However it does seem that Elvish libido and fertility were things that, like vacuum packed food, had a potentially indefinite shelflife when unused didn't keep long once opened, not quite single use but only a few hundred years in a lifespan as long as Arda...