There are several reasons why Mr. Dussel is disgruntled and unhappy. First of all, he was uprooted from his life and his home like everyone else. Before coming to live with Anne and her family, Dussel was a dentist. You can guess that he was a reasonably wealthy man with a comfortable living. He had to leave all of that to share cramped quarters, including a room with Anne. He would naturally be unhappy sharing a room with anyone, especially Anne. Anne is noisy and spunky, and she often sasses him. He misses his old life and although he was not married, he misses his girlfriend. He was separated from her because she was Catholic.