This is based on The Lay of Leithian (from The History of Middle-earth, Volume III) rather than The Silmarillion, but you can read this easily without having read that. The difference isn't overly drastic. The main change that affects this story is that Curufin is the mastermind of the brothers and the one who falls in love with Lúthien.

The events that I wrote about take place after the ban on Quenya by Thingol, so I have used Sindarin names.

I apologize for the awkward formatting in the first section.

Thanks to stick-at-nought shady for looking this over.

Breathe

For once, Fëanor's most eloquent son was wordless.

Curufin was struck to the soul with Lúthien's beauty. It was by far the deadliest knife that had ever pierced him, and he found himself struggling to keep his composure. His breathing became heavy and ragged; he hoped desperately that Celegorm could not see his distress. Her loveliness made him feel almost ill with lust.

As her own name and the name of her land left her lips, Curufin imagined running his hands through her dark hair. The smooth sensation was fairly unknown to him, but he speculated that it would feel something like...

. . .

... blood, streaming over his hands as he made his first kill. The slain of the Teleri had already started littering the ground, although they fought back valiantly to save their white ships. He had clasped his hand over the fatal wound of his nearly-dead foe, letting the hot blood flow over his fingers as fury pumped through his body...

. . .

Do not think of the Kinslaying! Curufin commanded himself desperately, taking a deep breath. You must be calm. Do not show your feelings; deceive the world into thinking that you have the power of deception. Think of your son, waiting patiently in Nargothrond and not believing any of your lies... But upon seeing Lúthien's bright, fearful eyes, all thoughts of Celebrimbor - even of Celebrimbor's mother - fled Curufin's mind. He wanted desperately to claim her body, and doing so, he would claim her soul. Her spirit would flee to the Halls of Mandos, leaving as quickly as...

. . .

... the Kinslayers - that was what they were called now - soaring over the water in the stolen ships of the Teleri. Standing on the deck and looking up at the white mast, silhouetted against the stark blackness of the night sky, Curufin was distracted momentarily by the ruthless eyes of Fëanor, glimmering from the breathtaking starlight overhead as the ships carved through the night-black sea. These were such beautiful ships, so abused for a purpose that, though dark, had to be righteous. It was all for the Silmarils; everything was for the jewels, and the Noldor were the moths that stupidly chased after the candles even though they had been blown out...

. . .

Curufin felt all too warm, even in the pleasant day, thinking of the many possibilities. The thought of taking her spirit - in a way, at least - was exhilarating, and it made a sadistic smirk appear on his face, curving his thin lips and bringing a cruel light to his eyes. She would be taken, stolen from Arda, her beauty gone. The most fair things died more rapidly than others; he thought of...

. . .

... the Silmarils, taken. Anguish was painted on Fëanor's face at the news of his father's death and the stealing of his precious Silmarils. He had lost the things that he loved dearest; it was obvious to Curufin that he and his brothers were placed below the Silmarils in order of their father's love, even Curufin himself. Still, the pain in Fëanor's eyes made Curufin's stomach twist. Then the Spirit of Fire swayed, falling, lying on his face as if he had been suddenly killed...

. . .

This lust, this horrific need was rare among their kind, but Curufin did not dwell on that thought, although it lingered in the back of his awareness. Lúthien was so unbelievably fair in his eyes, so beautiful that any thoughts of deceiving Felagund were stowed away to be uncovered at a later time. He could smell the soft fragrance of the flowers that were entwined in her hair, and it burned at his senses until he felt slightly weak at the knees.

Yes, this is lust, he thought, and I am left with no feelings beside it: lust for her, and for the Silmarils. Or perhaps it is love, and this truly is Arda Marred, a world that can only produce twisted, maimed imitations of life. Still, among us, the blackened saplings that reach out for the light, there are a few golden blossoms staining the dark land.

Oh, Father, Curufin found himself thinking miserably, left with no words to express the conflict that he felt. I am nothing like you now, for you would never have allowed yourself to become a thrall to regret. The fire of my spirit is nothing compared to yours, and I cannot burn away the pain as you once did, if you could feel pain at all.

Curufin struggled, choking and gasping, his tongue lolling and his eyes bulging in his desperation for a breath of air to hit his lungs. His throat burned, and his eyes stung and watered. It would make a fine tale: Curufin, son of Fëanor, strangled to death by a mortal, vanquished by a mere Man! Beren - curse his name a thousand times over! - had always managed to coincidentally dance out of the hands of doom. This was a humiliating death that, in Curufin's eyes, would shame the house of Finwë, even perhaps his treacherous son. Briefly, he thought that he would either die from lack of air or from the shame of the entire situation.

The calluses on the Man's fingers chafed against Curufin's neck as he squeezed more vigorously. Gagging painfully, the Noldo thought of Celegorm - what was taking his brother so long to come to his aid? The sounds around him faded into a dull blur, and he could only hear the blood pulsing through his head. He no longer had the strength to fight back, to oppose the mortal in some way. His fingers clawed weakly at the Man's hands, but to no avail. All that he could see with this new, hazy vision were the mortal's furious eyes.

You attempt to take what will never be yours, the eyes spoke, blazing with a fire that Curufin was all too familiar with, having seen it in his irate father, and even in himself. The people of Nargothrond called you the Dispossessed, and this will never be limited to your precious Silmarils. You will never possess love, and you will never know it.

At those thoughts, he knew that the strength to fight back was leaving him. The impervious, intangible shield that he had wrought in his mind to cover his weaknesses was splintering, and his body was becoming weak, useless, his hands dropping to his sides. His head drooped to one side; he felt saliva on his face as it rested in the grass.

As the pain in his chest flared - do not give up, he pleaded to himself - he wondered what his father would have said upon seeing his beloved son killed in such an embarrassing way. Perhaps Fëanor would have only shaken his head in a gesture that mocked sadness. Curufin could already feel the shame burning into his spirit.

I have failed you, Father.

Well before dawn, Celegorm woke to a scream that was all too familiar.

It was a disgusting, retching noise, wordless, because the one screaming had no one left to scream for. Celegorm sighed, feeling too weary to wake his brother. Let Curufin sleep, he told himself. You can never wake him from this dream. His younger brother's face was tense in sleep, and, as the characteristic sign of his flashback, his fingers were twined around his own throat, pressing down. He thrashed wildly, caught up in the nightmare. The sight was almost sickening, causing a frown to crease Celegorm's forehead as he turned away. I can do nothing for you, brother, he thought sleepily. You are like Father; you are too proud to slay yourself, even in a dream.

Though the irony left a bitter taste on his tongue, Celegorm could not bring himself to remember much about that fateful day without feeling sickened. It was simple to remember the mad grin on Curufin's face as he urged his horse into a gallop. The wind from their speed, which sent the light strands of Celegorm's hair flowing and whipping across his face, could not disguise his brother's reckless laugh. Celegorm remembered how Curufin had hoisted Lúthien onto his his horse, the muscles in his arms bulging as she struggled. The look of lust on the younger Noldo's face had been triumphant to the point of insanity, until Beren had cried out and leaped onto the horse, shoving Curufin to the ground. Then there had been a short, strangled cry, most uncharacteristic coming from Fëanor's fifth son, and from there on, things had turned ghastly.

Beyond that point, Celegorm was hesitant to recall the pure, unrivaled horror that had shot through his heart as when he saw his brother - did that word still hold love, after all that had passed? - struggling uselessly, pinned to the ground by the Man. Curufin's face had gone from pale to a disgusting purple, and Celegorm remembered how his eyes had bulged and his tongue had hung out uselessly as Beren's hands clamped around his throat.

Minutes later, as Curufin drew back the bowstring a second time and aimed his arrow at Lúthien, he had whispered a few hoarse words, his face twisted in pain at each syllable. "Better to have love die than to have it taken away," he had hissed, his voice raspy, but Beren had let the arrow strike him instead. No, the one that Curufin had thought he had loved was undying, and it was a heavy burden.

But the most pain in Celegorm's remembrance came from thinking of the ride away from the site of the conflict. Curufin had still been gasping for air, and he was limp, slumped up against the horse's neck, trembling. Celegorm, not knowing what to say, had tried to comfort his brother, to tell him that he was safe and that he himself would have speared Beren if it hadn't been for that damned dog of his, but Curufin had sat up suddenly and spat with a still-fragile voice, "You have never known pain, and I hope by the Valar themselves that you will! You are nothing but a coward, a pathetic, naive coward!"

No, you are wrong; I have known pain, Celegorm thought as he closed his eyes again, hearing his brother fall victim to another bout of choked screams. I knew pain when Father died, cursing Morgoth thrice with his last breaths and begging us to keep their oath, to avenge him. I knew pain when I saw Morgoth's iron mountains in the distance, wondering if the wind had caught the last ashes of my father's body on my skin. I knew pain in the days after Maedhros returned from Thangorodrim, and we knew deep inside that he was wondering, "Why did you not think to rescue me from imprisonment, when I would have been spared so much agony?"

I knew pain - oh, though I wish I could not have felt it! - when I thought that I would have to watch my brother die.

After unwillingly slipping back into a deep sleep despite his brother's distress, Celegorm heard whispers of Quenya in his mind as he again found wakefulness. Hearing the tongue of Valinor's peaceful days was bittersweet, and he relished the music of the language with closed eyes until he made out the words. The speaker sounded to be distraught, speaking of death and blood in a low, panicked voice.

"Curufin?" Celegorm asked, feeling useless as he listened to his brother's deranged whispers. "Curufin," he repeated, with more urgency, "if you are heard speaking that tongue, then..." His voice trailed off; he did not know exactly what would be done, but he was sure that any punishment would be increased exponentially if a son of Fëanor was involved. Normally, they spoke the so-called 'tongue of the Kinslayers' on a regular basis together, but somehow, this situation felt oddly tense, almost as if they would be caught.

Amid the soft Quenya, Curufin gasped suddenly, leaning down with his head in his hands and his back to his brother. Celegorm stood, cautiously nearing Curufin and facing him. Several glistening droplets clung to Curufin's fingers, sliding down his famously skilled hands and into his lap. With shock, Celegorm realized that Curufin's erratic, heavy breathing was due to his weeping. It seemed impossible: Curufin, crying; Curufin, grieving!

The most unnerving thing was how closely Curufin resembled Fëanor. The shared features between father and son made Celegorm feel eerily as if he was watching his father cry. The thought of Fëanor succumbing fully to grief was foreign to him. Pain had only made Fëanor furious at the cause of his own agony, and Celegorm had thought this to be true for his fifth son. Perhaps this was a rare exception. The thought of his deceased father made Celegorm hesitate before speaking again. Before he could, however, Curufin spoke louder, almost at a shout, and lifted his head. His voice was tight was pain.

"I could not breathe!" he spat in slightly accented Sindarin. His eyes were bright in the light of the moon with an injured sort of fury, and his hair hung in unwashed tangles around his ashen face. Moments later, he bent again with a bout of sobs that made his shoulders heave, but not before Celegorm noticed the hollow horror in his eyes, as if he was looking back on dark memories.

Celegorm shivered, although the night's temperature was pleasant and the day was coming swiftly. No day would fully illuminate the darkness that lingered inside of the sons of Fëanor, and no light of the sun or moon could make up for the loss of true light.

Breathe, Curufin, my brother, he thought. To avenge our father, for the sake of our legacy, for the Silmarils, breathe.

Curufin could not remember exactly how he had been injured, and his memories were seeping out of him along with the blood. He could barely recall the way out of Menegroth's maze of caves. It all seemed so unbalanced, so dark. Finally, he escaped, darting through the swords and hating their grating clash that rang in his ears, and collapsed beneath the nearest tree. The chill of the winter made him shiver heavily.

His own blood, crimson and hot against his hand, seeped through his fingers. The wound to his stomach would heal eventually, though with an ugly scar, but there was no possible healing for the arrow in his right eye. Curufin had turned to be suddenly struck by a searing flash of pain, and Celegorm had shouted in horror from nearby, but Curufin had been blinded momentarily, his vision reeling and his mind swimming. His right eye was still unseeing, wrenched open, the shaft of the arrow still protruding out.

Perhaps we were meant to die in the end, he thought, slumping against the tree in defeat, staring at the trail of his own blood leading back into Menegroth. A trail of the scarlet liquid dribbled from his mouth, and he coughed. "It is for the Silmarils; for the Silmarils," he repeated aloud, shocking to hear the garbled tones of his usually reliable voice. It was all too much like those dark, familiar dreams, and reminiscent of the event that had inspired them. Fingers clawing at his throat, a pair of furious eyes, his body becoming limp as if he was falling asleep...

Lúthien's face, beaming out like sunlight glinting on rain; her hair, a dark river flowing to the sea. Her eyes, wide and afraid, not needing the light of Aman to contribute to their brightness. Her mercy, begging Beren to spare Curufin's life, only making him long for her all the more. And now... dead, dead for a Man!

Curufin coughed into his elbow, feeling warm blood slide across his armor. He reflexively wrenched his eyes shut as he did so, causing a flash of pain from the location of the arrow wound. With the fey madness that always seemed to precede death, he gripped the blood-slick shaft of the arrow, attempting to pull ruthlessly. However, the pain left him weak, and his trembling hands felt useless. If an adversary were to come upon him now, he would be granted an early death. He felt as helpless as he had back in those blissful, agonizing days in Nargothrond on which he would be given a tantalizing glimpse of Lúthien's face...

She was a Silmaril, Curufin thought spitefully. She was a Silmaril: a perfect light, seducing us, driving us mad, unknowingly whispering for us to do anything, anything, to claim her. Now, nothing can bring back the light. We followed blindly, but in the end, death always conquers the undying. We were yearning for a light that we knew was unreachable, and we still know that, in the end, the things that we love will only bring pain. We lust for the light that will burn us.

But if this is to be a tale of lust, let the world know that I believed it to be love.