Boo Radley lives a lonely life. He is isolated and locked away from other people. No doubt, Boo lives a lonely life being kept away from society. He is withdrawn into his own world. Boo stays indoors most of the time. Rarely is he seen outside.
When Boo begins leaving gifts, trinkets, in the knothole of the tree, he shares his feelings with Scout and Jem. This is a way he can show kindness to Jem and Scout. As Jem and Scout are enjoying their communication with Boo, Nathan Radley, Boo's father, fills the knothole with cement, putting a stop to any type of relationship that Boo was building with Jem and Scout. Once again, he withdraws to his lonely world.
Another instance of loneliness is when Scout feels left out as Jem and Dill grow closer. Jem and Dill decide to go swimming. They inform Scout that she cannot go for they will be swimming without their clothes. Scout does feel lonely and left out. She turns to Miss Maudie for comfort.