I’m sorry to hear that.
I don’t know – This is such a pessimistic, one-dimensional and bleak assessment? You are absolutely entitled to your opinion, but I entirely disagree. I believe that Thorin in fact gets some of the very funniest moments, and can show levity, affection and selflessness even when he is in distress. He is an ENDLESS fount of comfort for Frerin, and shows more consideration for his mother, brother’s, Gimli’s, Fili’s and Kili’s and Bilbo’s feelings than for his own. He is unhappy at times, yes. But that’s not all he is.
Mental illness has nothing to do with it. He is winning. He is learning to manage himself, he is a success story, not a tragedy.
He is comforting. He builds people up. He grows, he learns, he fixes his mistakes. His family support him, certainly – but he supports THEM right back. Fili, Kili, Frerin, Fris, Thrain, Thror, even Hrera – he gives every single one of them comfort and help and love. He is not a drain of love, sucking their support and energy away. He is a rock for them: they follow his lead.
And yeah, he is funny.
For example: actual lines Thorin says in the fic, from Chapter 33:
Around him, the star-lined figures of Dwarves came fading into the gloom, and Frerin pushed through them to stand stock-still beside Thorin at the sight before them. “Thorin!” he said in dismay.
“I have kept my temper,” Thorin told him, fighting the twitching of his lips.
“What have you done?”
“What should have been done in Edoras,” Thorin said, and he threw a companionable arm around his little brother. “You know, these darksome unwholesome holes might actually become a favourite place of mine?”
“You are not funny,” snapped Frerin.
“I am hilarious,” said Thorin, perfectly straight-faced.
(from Chapter 35)
And then the Dwarf, evidently rather embarrassed by his recalcitrant mop, grabbed the brush from the dresser. The dresser that Bilbo was seated upon. His hand passed straight through the Hobbit’s leg!
Bilbo’s eyebrows shot back up to his hairline, and he could feel his face falling into its most Baggins expression as Thorin slowly turned back to look at him. “Again, my apologies,” he managed.
“You are not making a terribly good fist of this, are you,” Bilbo said, and it was not a question. Thorin winced, making no effort to hide it, and he sat back upon his pallet and fiddled with the brush in his hands.
“Apparently not,” he said ruefully.
(from Chapter 25)
“I am working, ‘amad!” he said, and Thorin settled back, folding his arms, to watch the show. “It is Frís’ name-day soon, and…”
“Oh, that is sweet, darling, but do try to remember that you have a mother,” she said, and pulled at the vast braids of Thráin’s beard. “Tsk. Shocking. Look at what you have done, you smell like a foundry and you look like a highland sheep! Thorin, don’t you start smirking over there, my lad, your hair is a disgrace.”
“Grandmother!” Thorin protested, and resigned himself to being forever twenty-four in her eyes and no older. It was infuriating.
“Best not to fight it, inùdoy,” sighed Thráin as Hrera began to comb out his working-braids, muttering to herself all the while.
“I learned that lesson long ago,” Thorin agreed solemnly, and jerked as Hrera pinched his elbow with her long, silver-tipped nails.
“Pair of upstarts,” she huffed. “Wait there for your turn. I won’t have my family looking like a bunch of ruffians. Longbeards! What are you like!” she exclaimed, and gave Thráin’s hair a particularly vicious combing. His eye twitched.
When they finally escaped, Thráin’s hair had been smoothed back into a neat barrel plait, and his beard had been worked into two intricate weaves that fell either side of his great deep chest. Thorin’s hair had been pulled up and given a thorough oiling (“Just look at this! Disgraceful!”) and then Hrera had spent quite some time lamenting the spray of grey at his hairline before weaving a thick braid from the top of his head to hang down his spine, leaving only his side-braids to hand before his ears.
Thráin and Thorin looked at each other. “I won’t laugh if you won’t,” Thráin said with the utmost solemnity.
“These terms are acceptable,” Thorin returned gravely, and then they carefully avoided looking at each others’ face for the next ten minutes.
They finally found Thrór in the dining hall, though his head was bent over a piece of paper and no food was to hand, only a jug of ale.
(from Chapter 13)
“What?” cried Gimli, shocked out of his silent contemplation of the ruin of Khazad-dûm, stately and beautiful even in decay. “That was a kingly gift!”
Thorin fought the urge to squirm under the sudden attention of three dead Dwarves and a Wizard.
“Yes,” said Gandalf, smiling. “I never told him, but its worth was greater than the value of the whole Shire and everything in it.”
“You can all stop looking at me now,” Thorin growled.
“Aye, leave him alone,” Balin said, trying and failing to keep the amusement from his voice. “He’ll be as cross as a bear with a sore paw otherwise.”
“You mean he can be otherwise?” sniggered Óin, and he ducked as Thorin swiped at him with a fist. “Ah, too slow, my King. Do I get a pretty mithril prize?”
(again – chapter 25)
Thorin shrugged off the clinging starlight, and held up his arm. “Here, namadul, lean on me.”
Kíli looked up with startled, red-rimmed eyes and nearly fell off the hillock he was perched on. “Oh my Maker,” he gasped, pressing a hand to his chest. “You scared the life out of me!” Then he pulled a face. “Well, when I say life…”
Thorin’s lips twitched. “Most droll. Come, you look dreadful.”
There are lots lots LOTS more – which you will discover, should you read the story.
As to the question, “do dwarves ever feel bad if their personalities are more pessimistic and less cheerful etc.” I don’t think you really wanted an answer to this.