Just watched the sad (terribly sad!) clip from the extended edition! :'( Thorin's face when he hears Lord Elrond speak of the sickness and what it did to his grandfather and father... Anyway, this story is based on that clip!
"Are you alright?" Bilbo hesitantly asked, approaching the visibly wounded dwarf. "I know you heard what Lord Elrond and Gandalf said, and I was only wondering if you were alright."
Thorin didn't answer. Instead, he kept his eyes trained on the elven city before him. "No one can be 'alright' from that," came when he finally spoke, his voice dry and cracked.
Bilbo nodded. "So... you're not okay with what Lord Elrond said?"
The dwarf heaved a heavy sigh. "I have no choice," he replied. "It's true. That sickness lives within my family... My grandfather and father died from it. I can't reclaim Erebor knowing I'll make those same cursed mistakes they did." He let out another sigh, this one sounding more hurt than the other. "I have no choice, Master Baggins. I know it'll happen."
"Then why can't you just stop this quest if you're so dreading it?" Bilbo asked.
Thorin's eyes darkened. "My people need their rightful home, and I am the last one in line to do so," he growled. "Since the dragon attacked Erebor, our people have been lost and without a home. I am the only one determined enough to return to our home."
"Balin told me you had lived in the Blue Mountains," Bilbo began, treading lightly on this complicated subject. "He said the dwarfs were happy there... W-why then..."
"As a king, you want the best for your people," Thorin started, looking down at his boots. "I wasn't able to give my people their kingdom... Yes, I built a new kingdom in the Blue Mountains, but it wasn't the same as Erebor. Nothing will ever be the same as Erebor."
Bilbo nodded quietly and started to walk to the room the elves gave him. He made two steps in before he turned around. "Thorin," he said with a sigh.
The dwarf looked up.
"I do hope you don't succumb to the sickness," Bilbo honestly spoke. "You're too great of a leader to fall into such madness."
"Thank you," Thorin replied, his voice barely cracking. He nodded and watched Bilbo head for the room. He breathed a heavy sigh and looked out at the city. "I fear... I will fall," he spoke to no one in particular.