Elves, immortality and reproduction
 

As far as I can calculate, Celeborn and Galadriel were an "item" for at least 5,000 years, maybe longer.

Now Elves don't age - and Galadriel was by all accounts a very attractive female - and presumably Celeborn liked to sleep with her. So how come they and other Elven couples didn't have kids continuously throughout the ages ? Even at the comparatively modest breeding rate of one child every 10 years, why didn't Celeborn and Galadriel not have at least 500 children ?

It's all explained in Morgoth's Ring. Elves give part of their spirit to their children. Which is why Feanor's mother Miriel was absolutely knackered after giving birth to such strong, energetic spirit. So after a few children (Feanor's 7 was the greatest number in history I believe) they lose enthusiasm for more so they devote their attentions to other Elvish pastimes like singing and looking down on dwarves. :Merisu:

Whether they still sleep with each other when they stop having children I'm not sure. Maybe they only have sex for procreation or maybe they can choose whether they want to have children or not when they have sex - no unwanted Elvish children. Tolkien doesn't seem to be a fellow too keen on contraception though.

Elves are the Catholic Church's ideal subjects, always keeping their hands to themselves and on top of the blanket, unless they're in in for the money so to speak. Whether this causes frustration for Celeborn or not is anyone's guess.

As Elmo says, it's all explained in Laws and Customs of the Eldar in HoME X.

MoS, there's an old thread on this subject you may like to look up (if you haven't found it yet). Lots of discussion and speculation there to fuel your imagination!