Erotic Tolkien

Then Beren and Lúthien went through the Gate, and down the labyrinthine stairs; and together wrought the greatest deed that has been dared by Elves or Men. For they came to the seat of Morgoth in his nethermost hall that was upheld by horror, lit by fire, and filled with weapons of death and torment. There Beren slunk in wolf's form beneath his throne; but Lúthien was stripped of her disguise by the will of Morgoth, and he bent his gaze upon her. She was not daunted by his eyes; and she named her own name, and offered her service to sing before him, after the manner of a minstrel. Then Morgoth looking upon her beauty conceived in his thought an evil lust, and a design more dark than any that had yet come into his heart since he fled from Valinor. Thus he was beguiled by his own malice, for he watched her, leaving her free for a while, and taking secret pleasure in his thought. Then suddenly she eluded his sight, and out of the shadows began a song of such surpassing loveliness, and of such blinding power, that he listened perforce; and a blindness came upon him, as his eyes roamed to and fro, seeking her.

(J.R.R.Tolkien: The Silmarillion)

an evil lust. That, to my knowledge, is the only reference of an erotic or sexual nature in the entirety of Tolkien's work. It's curious that the only character to whom is explicitly attributed some kind of sexual pulsion is the personified incarnation of Evil...

Given Tolkien's fondness for the finnish and icelandic languages, and for old norse sagas, he should have taken a bit of inspiration from Njal's Saga:

"I would like to be divorced from Hrút, and I can tell you what particular reason I have for it. He is not able to have marital intercourse with me in any such manner that I can enjoy. In all other respects he has the the ways of other excellent men."

"I don't quite understand," said Mord; "be more specific."

She answered: "Whenever he comes to me in bed his member is so large that he cannot gratify himself with me; and yet we have tried all ways to have intercourse, but always unsuccessfully. Yet before we part he shows that he is as passionate as other men."

(Njal's Saga)

An episode like that in the Arwen-Aragorn storyline would have greatly improved The Lord of the Rings, in my opinion.