Author's Notes: There are two characters named Gelmir in The Silmarillion - the first is Gwindor's brother. The second is one of the messengers sent to Nargothrond by Círdan. Tolkien does not say which of Guilin's sons is the eldest.
I've used 'Arothir' rather than 'Orodreth' in this story, based on Tolkien's last genealogy for the sons of Finarfin. (1)
Disclaimer: Tolkien owns the characters and plots. I'm just playing in his garden.
Greater Woe than if That Field Had Not Been Fought
With them they brought Gelmir son of Guilin, a lord of Nargothrond, whom they had captured in the Bragollach, and had blinded; and their heralds showed him forth... . And they hewed off Gelmir's arms and legs, and left him. (2)
'I am sorry for your loss.' Well-meaning as might have been the speaker, his tears were spent, and he could find no more.
At each loss, he had thought his heart must break - this time, he would shatter - yet somehow, the sun and moon continued to rise and set and so did he.
The horror of his younger son's torment, of his final, unthinkable moments, became, in the mouths of others, only a footnote to his elder son's death in the bowels of Thangorodrim. But that singular comfort, that he had no child left to lose, was not to be his, and he took no comfort in Gwindor's unlooked-for return.
Out of his suffering had come great wisdom, but wisdom no longer held a place of honour among the Eldar. In the days when Celegorm and Curufin held sway, the heart of Nargothrond had turned to darkness, and its poisoned darts slew Elf and Adan, Easterling and Orc alike. Arothir had at last won the upper hand, but the people remembered their cowardice, and the desertion of beloved King Finrod, and shame burned like bile in their mouths. (3)
"I cannot blame them for hearing Túrin's promises of glory. We have seen naught but defeat for so long. But his glory is fleeting - he will lead us only to more sorrow. Even with all the might of Elves and Men, even were we not at war amongst ourselves, we could not overcome Morgoth. We must put our hope in the West."
Though the lords of the King's council would not hear him, Guilin drew pride in his son's courage. Yet so dearly bought was that pride that he wished it would not have been, and that his once rash and beautiful son would have found an honourable death instead.
For all the light had gone out in Gwindor. The Elf who had captured the heart of the King's daughter - the Elf who had rallied the Noldor in the Nirnaeth Arnoediad - had returned as like unto an aged Man. Crushing labour had bowed his back and withered his fair face; his escape had cost him a hand and his arm pained him long after its healing. Worse still was the reflection of his ruin in the eyes of the lady who had once loved him.
A great army now massed in the North, for such were the wages of Túrin's glory - Nargothrond, so long passing unnoticed by secrecy, had been made known to Morgoth. Guilin sent his wife to the Havens, but remained at arms in defence of the city, for he could not desert his king.
"We are utterly lost, Adar," Gwindor said, as the host mustered at the bridge. "They were not at the Nirnaeth; they have not seen the great armies under Thangorodrim. The enemy cannot breach Doriath, and Túrin's father will not betray Gondolin. But Morgoth has the city under the hill in his grasp, and believe that he will send all his might against it."
Unsaid, but understood: Gwindor did not intend to return this time. Under the Doom, there was no hope of healing but in death.
She was waiting for him on the quay at Balar.
"He is gone?"
"Yes."
"You are certain?"
"Yes."
"Good."
They shared a long look then, more regret than grief, and then she tucked his arm under hers.
'I am sorry for your loss.' But it was no loss. There were worse fates than the halls of Mandos. They went forward with peace in their hearts.
(1) Tolkien's last genealogy for the sons of Finarfin
(The Peoples of Middle Earth, 'The Shibboleth of Fëanor' p 350-351 pub Houghton Mifflin)
(2) With them they brought Gelmir son of Guilin
(The Children of Húrin p 55 pub Houghton Mifflin Kindle Edition)
(3) the heart of Nargothrond had turned to darkness
...But with stealth and ambush, with wizardry and venomed dart, they pursued all strangers, forgetting the bonds of kinship. Thus they fell from the valour and freedom of the Elves of old, and their land was darkened.
(The Silmarillion p 167 pub Houghton Mifflin Kindle Edition)
I hadn't read this passage all that carefully before now. I can see that they might shoot first and ask questions later when it came to Men, but no Elves were ever allied with Morgoth (unless they were under his spell as thralls). I would guess that the brothers suggested this after they captured Lúthien, fearing enquiries from Doriath. (My bet is on Curufin as the author of that particular policy.)