In The Hobbit why are the dwarves happy and why is Bilbo unhappy?

The dwarves were cheerful because they had finally taken their kingdom of the Lonely Mountain after the great dragon Smaug was defeated by the Lake men. Bilbo was unhappy because when he was back at the shire, he always wished to go back and see the dwarves of the Lonely Mountain and wander the paths of Mirkwood.