What LaCE actually says is:

a) Elves marry only once (Finwe aside).

b) Elves are seldom swayed by the desires of the body only (the context being that they seldom have cause to break their betrothals).

c) An elvish marriage is made by the act of bodily union and the exchange of oaths by the name of the One.

What it never quite says is that the act of bodily union can only occur in marriage. That's probably because Tolkien took it as read - but he never wrote it.

It's also not said that bodily union and the desires of the body are intended only for the creation of children. Again, he kind of assumed it, but never quite said it. He almost says it when he writes:

The union of love is indeed to them great delight and joy, and the 'days of the children', as they call them, remain in their memory as the most merry in life; but they have many other powers of body and of mind which their nature urges them to fulfil.

But that doesn't actually say that they give up the 'union of love' (oh, Tolkien and his euphemisms!) when they stop having children.

And - you guessed it - he never bothered to say that neri and nissi would only be drawn in love to one another, not to others of their same kind.

My personal assumption is that in Valinor things went basically as people usually read it - elves are celibate until marriage, marry someone of the opposite sex, have children, and then give up That Sort Of Thing to focus on other pursuits. In Middle-earth, where life goes by much faster and people keep doing inconsiderate things like 'dying' or 'not having the resources to start a 144-year art project', they likely loosen up a little. They still only marry once - but before marriage, or after their spouse is gone, they Make Their Own Entertainment (hem hem).

hS