Bilbo instantly knew Thorin was approaching him by the sound of his footsteps hard and swift. Bilbo put up his polite smile and turned to face him, he'll have to be step ahead of him. Don't want to be caught in unwanted thoughts.
"Oh Thorin" Bilbo started his prepared speech of his own departure but he never seemed to manage get the right words out. Thorin's stare made it difficult to think of the right phrase, it seemed easier while he thought about it in solitude. Things got worse when Thorin declared scarcity of the given word and went on to picture himself striding into the flames. That image Bilbo considered deeply disturbing, he would be smarter than that, would he?
"Stealth is a better way" Bilbo tried to argue with him but only got him to get angry. Bilbo got angry too so when Thorin challenged him to say out loud he's giving up Bilbo withdrew.
"I think all is said" Bilbo turned away from him. Thorin saw no value in him, there was no need to humiliate himself further by declaring his departure. He would have left Bilbo behind anyway. Everything suggested to that, and since Trolls it was all too clear.
Bilbo expected of him to just leave it at that but them Gandalf and Elrond came to sight. As their voice came towards them Bilbo realized they are discussing Thorin. Bilbo looked him with corner of his eye hoping he would leave, it was always best not to know what exactly people are saying about you when you're not around. You could imagine it pretty lively anyway, there was no need in hearing it. People were keen in saying things just to say them, they rarely thought it through.
But this were wizard and an elf maybe it won't be that bad.
It got worse. As they spoke of madness in Thorin's family Bilbo tried to stay detached, that didn't concern Bilbo. It was just an awkward moment and he needed to look forward to avoid acknowledgment that anything happened, to let Thorin keep his dignity. As they went out of sight Bilbo turned to say sometning meaningless and polite to Thorin but he had left. His departure was so swift Bilbo didn't notice it.
As he looked at the empty space he just knew Thorin is leaving Rivendell in this moment. He was that kind of a dwarf, he wouldn't stay and pretend that he hadn't heard anything disturbing.
That was it them. He'll never see Thorin Oakenshield again. He stood there for a moment longer looking around to all that beauty and felt nothing towards it. On the lower path appeared pair of elves. Bilbo looked at them and their grace and beauty but felt nothing towards it. They were beautiful and cold like distant stars. They hadn't had a burning flame that was lit behind Thorin's eyes.
Bilbo stood there trying to erase those eyes from his mind but when that was accomplished he felt like the world became empty and hollow place. He thought about Thorin striding towards Lonely Mountain, about dragon's flames, of his solitude and in the end of the madness.
Thorin couldn't go mad, or could he? Maybe Gandalf is right maybe someone so small like him could make some difference in the end. What if his departure means their defeat in the end? What if lack of his sound reason and some wit makes the difference between mad Thorin and sane one? Maybe his contribution won't be a big one, but still important enough on the scale of things to keep Thorin sane and in safety of his home.
That made Bilbo hurry. He could never be at peace in his own home imagining thirteen of them in the cold, wet, or in the flames. He'll have to see the end of this to have a peace of his own.