[HerenIstarion]

(Laws and Customs among the Eldar)

The Eldar wedded once only in life, and for love or at the least by free will upon either part. Even when in after days, as the histories reveal, many of the Eldar in Middle-earth became corrupted, and their hearts darkened by the shadow that lies upon Arda, seldom is any tale told of deeds of lust among
them.

Marriage, save for rare ill chances or strange fates, was the natural course of life for all the Eldar. It took place in this way. Those who would afterwards become wedded might choose one another early in youth, even as children (and indeed this happened often in days of peace); but unless they desired soon to be married and were of fitting age, the betrothal awaited the
judgement of the parents of either party.

In due time the betrothal was announced at a meeting of the two houses concerned, and the betrothed gave silver rings one to another. According to the laws of the Eldar this betrothal was bound then to stand for one year at least, and it often stood for longer. During this time it could be revoked by a public return of the rings, the rings then being molten and not again used for a
betrothal. Such was the law; but the right of revoking was seldom used, for the Eldar do not err lightly in such choice. They are not easily deceived by their own kind; and their spirits being masters of their bodies, they are seldom swayed by the desires of the body only, but are by nature continent and steadfast.

Nonetheless among the Eldar, even in Aman, the desire for marriage was not always fulfilled. Love was not always returned; and more than one might desire one other for spouse. Concerning this, the only cause by which sorrow entered the bliss of Aman, the Valar were in doubt. Some held that it came from the marring of Arda, and from the Shadow under which the Eldar awoke; for thence only (they said) comes grief or disorder. Some held that it came of love itself, and of the freedom of each fea, and was a mystery of the nature of the Children of Eru.

After the betrothal it was the part of the betrothed to appoint the time of their wedding, when at least one year had passed. Then at a feast, again shared by the two houses, the marriage was celebrated. At the end of the feast the betrothed stood forth, and the mother of the bride and the father of the bridegroom joined the hands of the pair and blessed them. For this blessing
there was a solemn form, but no mortal has heard it; though the Eldar say that Varda was named in witness by the mother and Manwe by the father; and moreover that the name of Eru was spoken (as was seldom done at any other time). The betrothed then received back one from the other their silver rings (and treasured them); but they gave in exchange slender rings of
gold, which were worn upon the index of the right hand.

Among the Noldor also it was a custom that the bride's mother should give to the bridegroom a jewel upon a chain or collar; and the bridegroom's father should give a like gift to the bride. These gifts were sometimes given before the feast. (Thus the gift of Galadriel to Aragorn, since she was in place of Arwen's mother, was in part a bridal gift and earnest of the
wedding that was later accomplished.)

But these ceremonies were not rites necessary to marriage; they were only a gracious mode by which the love of the parents was manifested, and the union was recognized which would join not only the betrothed but their two houses together. It was the act of bodily union that achieved marriage, and after which the indissoluble bond was complete. In happy days and times of peace it was held ungracious and contemptuous of kin to forgo the ceremonies, but it was at all times lawful for any of the
Eldar, both being unwed, to marry thus of free consent one to
another without ceremony or witness (save blessings exchanged
and the naming of the Name); and the union so joined was alike
indissoluble. In days of old, in times of trouble, in flight and
exile and wandering, such marriages were often made. [Thus Beren and
Tinuviel could lawfully have wedded, but for Beren's oath to Thingol.]

The underlined sentence probably expressing the following:

(Ephesians 5:28-5:30)

28 So ought men to love their wives as their own bodies. He that loveth his wife loveth himself. 29 For no man ever yet hated his own flesh; but nourisheth and cherisheth it, even as the Lord the church: 30 For we are members of his body, of his flesh, and of his bones.

also

Corinthians 6:16 - What? know ye not that he which is joined to an harlot is one body? for two, saith he, shall be one flesh.

also

Mark 10:8 - And they twain shall be one flesh: so then they are no more twain, but one flesh.

The meaning being, the mere act of love is enough for the 'flesh' to become 'one', the rest being rituals

So, in Elves Tolkien was making 'real' what he held to be real for humans: sex is an act of marriage.

Aragorn and Arwen: I do not suppose they were 'doing it':

Compare wording, btw:

(In Lorien, Aragorn aged 49)

But Aragorn answered: "Alas! I cannot foresee it, and how lit may come to pass is hidden from me. Yet with your hope I will hope. And the Shadow I utterly reject. But neither, lady, is the Twilight for me; for I am mortal, and if you will cleave to me, Evenstar, then the Twilight you must also renounce."

'And she stood then as still as a white tree, looking into the West, and at last she said: "I will cleave to you, Dúnadan, and turn from the Twilight. Yet there lies the land of my people and the long home of all my kin." She loved her father dearly.

with:

Matthew 19:5 - And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?

(Consciously so in the revision )

That was a side note, to back me up in my quoting of the New Testament. Now for the 'doing it':

Rivendell, Aragorn aged 20

'But Elrond saw many things and read many hearts. One day, therefore, before the fall of the year he called Aragorn to his chamber, and he said: "Aragorn, Arathorn's son, Lord of the Dúnedain, listen to me! A great doom awaits you, either to rise above the height of all your fathers since the days of Elendil, or to fall into darkness with all that is left of your kin. Many years of trial lie before you. You shall neither have wife, nor bind any woman to you in troth, until your time comes and you are found worthy of it."

and also

(Rivendell, Aragorn aged around 50)

My son, years come when hope will fade, and beyond them little is clear to the. And now a shadow lies between us. Maybe, it has been appointed so, that by my loss the kingship of Men may be restored. Therefore, though I love you, I say to you: Arwen Undómiel shall not diminish her life's grace lot less cause. She shall not be the bride of any Man less than the King of both Gondor and Arnor.

and finally

And at last when all was done he entered into the inheritance of his fathers and received the crown of Gondor and sceptre of Arnor; and at Midsummer in the year of the Fall of Sauron he took the hand of Arwen Undómiel, and they were wedded in the city of the Kings.

'Took the hand' implies it was a first time.

cheers