It was impossible to not see the advantage of a union with Thingol's people. With the might of Doriath behind them, an attempt to regain the silmarils stood a chance of success. Cufurin may have been the crafty one, but Celegorm wasn't stupid. He recognized the opportunity Huan had plopped into their lap.
"It has to be you," Curufin murmured as they watched Lúthien sleep. "I'm married."
Celegorm nodded. "I know."
"You don't look excited. Isn't she beautiful?"
"Yes, but..." Celegorm frowned, watching as Lúthien sighed in her sleep, curling up closer to Huan. "This will not be easy, brother."
"Let me free!" Lúthien demanded, banging upon the door. Standing outside, Celegorm scowled.
"You will be free if you choose to stand by my side," he said. "I have already sent word to your father of our engagement."
"My father would sooner disown me than allow me to wed a son of Fëanor!"
"He will choose a Fëanorian over a mortal," Curufin said.
Lúthien screamed, and a blast of cold air chilled Celegorm to the bone. He flinched, grabbing his brother's hand and dragging him away.
"She's a Maia witch," Celegorm hissed. "If she escapes..."
Curufin scowled. "She will not."
He covered his head, stepping lightly as he could in the darkness. Curufin would say that he'd been bewitched, but it was his heart that had changed. Capturing maidens and forcing himself upon them... He may be a Kinslayer and a thief, but Celegorm was not this kind of man. Curufin did only what he saw as necessary, he knew that, but Celegorm could not act with such cruelty.
He heard her singing softly in her chamber, telling Huan her tale of woe. His hound turned to him, a question in his eyes.
Celegorm nodded sheepishly, and unlocked the door.