What quotes from The Catcher in the Rye show that Holden is depressed about his brother, Allie?

In chapter five, as Holden is thinking about what to write for Stradlater's composition, he decides to write about his younger brother's baseball mitt. This opens up the discussion about Allie and how he died from leukemia in 1946. He explains that Allie was two years younger, intelligent, and very kind. He goes on tell about he reacted to Allie's death, which is depressing as well as self-destructive:

"I slept in the garage the night he died, and I broke all the goddam windows with my fist, just for the hell of it. I even tried to break all the windows on the station wagon we had that summer, but my hand was already broken and everything by that time, and I couldn't do it" (39).

The above passage shows Holden acting out because of his grief, anger, and sadness over his brother's death. Then, in chapter 22, Holden is talking to his sister Phoebe about something that he actually likes in life. His answer is Allie, which is depressing because as Phoebe reminds him, "Allie's dead." Holden responds with the following:

"I know he's dead! Don't you think I know that? I can still like him, though, can't I? Just because somebody's dead, you don't just stop liking them, for God's sake--especially if they were about a thousand times nicer than the people you know that're alive and all" (171).

Clearly, Holden is always depressed about Allie because he thinks about him continually. And what he thinks about is that Allie is the only nice person he's ever known. As a result, Holden doesn't trust or respect many other people in his life and he suffers for it. 

Finally, after leaving Mr. Antolini's apartment in chapter 25, Holden is walking around New York lonely and not knowing where to turn next. He thinks of Allie as he goes through a nervous breakdown. 

"Then I started doing something else. Every time I'd get to the end of a block I'd make believe I was talking to my brother Allie. I'd say to him, 'Allie, don't let me disappear. Allie, don't let me disappear. Allie, don't let me disappear. Please Allie.' And then when I'd reach the other side of the street without disappearing, I'd thank him" (198).

With this experience, it is almost as if Holden is praying to Allie to save him from his problems because he is completely lonely, depressed and lost. This shows that everything wrong with Holden can be traced back to Allie's death. If Holden had received the psychological and emotional help he needed at the time he lost Allie, he would not be in the situation that he's in. Holden needed to learn how to deal with this loss through therapy and love from home, which he did not receive. As a result. Holden is continually depressed about Allie's death.