This is a tough question to answer since Boo only speaks once during To Kill a Mockingbird and author Harper Lee (and Scout's narration) gives us virtually no information about Boo's inner thoughts and feelings. To correct several aspects of the previous post, Boo did attend school and was described as always speaking "nicely to me, no matter what folks said he did" by Miss Maudie. And Boo once had friends, and they were what caused his first problems with the law. He had begun to hang out "with the wrong crowd"--the Cunninghams from Old Sarum.
Boo must have learned eventually that there could be no real life for him outside his home. After being held prisoner in his house by his parents, the practice continued when his brother, Nathan, came to look over him following the death of old Mr. Radley. Boo may have known about the terrible rumors that were spread about him by his neighbors in Maycomb, and he must have felt safe in the outside world only when he prowled about at night. He undoubtedly desired human interaction, and he must have realized that the innocent Finch children were his best and closest source. They reacted positively to the gifts he left in the knothole of the oak tree, and he responded in kind: mending Jem's pants so he would not get in trouble with Atticus, and warming Scout with a blanket on the night of Miss Maudie's house fire. When the children gave up their attempts to get a look at Boo, Boo continued to keep an eye on them, as evidenced by his sudden appearance on the night Bob Ewell attacked them on Halloween.
Boo must have felt that, with Bob's death, his job as protector of the Finch children was done, since Scout never saw him again after she walked him home that Halloween night. I find it sad that Scout and Jem never paid him another visit, at least attempting to knock on the Radley door to see if he would greet them. Boo may have continued to secretly keep an eye on Jem and Scout, since it would be many years before they grew into adulthood, but Boo "with his shy ways," was at home only inside his house. Jem thought that
"... maybe he doesn't want to come out."
But it was probably more like Dill had predicted:
"Maybe he doesn't have anywhere to run off to."
Arthur (Boo) Radley's life experiences were limited because he was a prisoner in his own home, never allowed to go to school, have friends, get married, have children, or even hold a job. The people in the town have forgotten him, and the children fear him. With such surroundings, Boo would have been within his rights to be a bitter, angry man; however, he shows affection and compassion for Scout and Jem by leaving them small gifts and watching over them. Through his love for the children and his immense respect for Atticus, Boo learns to find the courage to save Scout and Jem in a profound and life-changing moment.