Dying Of The Light by George R.R. Martin
A whisperjewel from Gwen Delvano calls Dirk t'Larien across space and beyond the Tempter's Veil to Worlorn, a dying Festival planet of rock and ice. Warlorn is slowly drifting through twilight to neverending night; as the planet sinks into darkness, so its inhabitants face annihilation.
Seven years ago, on Avalon, Gwen was Dirk's lover, his Guenevere; now she wears the jade-and-silver bond of Jaantony Riv Wolf high-Ironjade Vikary, a barbarian visionary, an outcast from his own people for his acts of violence. And Garse Janacek, Jaan's *teyn*, his shieldmate, is also bound to Gwen - in hatred. Dirk, a rogue and a wanderer, is called to be saviour of the three who are bonded together in love and hate.
But in breaking their triangle, he could lose all ...