There are two specific instances in which Holden states that his problem is loneliness. The first is to be found at the end of Chapter 19 in which Holden is having drinks at the Wicker Bar with a pseudo-intellectual acquaintance named Carl Luce. The exact page number in my paperback copy is 149.
"Have just one more drink," I told him. "Please. I'm lonesome as hell. No kidding."
The second confession occurs in Chapter 20 when Holden is sick and drunk in the men's restroom at the Wicker Bar. The exact page number in my book is 153.
When I finally got down off the radiator and went out to the hat-check room, I was crying and all. I don't know why, but I was. I guess it was because I was feeliing so damn depressed and lonesome.
Throughout the novel Holden is driven by loneliness. He keeps trying to think of people he might call and get together with. He even tries to strike up acquaintanceships with total strangers, including a pianist who comes into the restroom at the Wicker Bar to comb his hair (on page 152). Unfortunately, Holden has a problem relating with anybody, so he remains lonely and frightened by his isolation. Holden is a misfit and an outsider. People don't understand what he wants from them. They seem to be satisfied with superficial relationships--almost as if they don't realize that any other kind of human relationships can exist. Perhaps they are right.
The thing that most tormented De Maupassant, to which he returns many times, is the painful state of loneliness, spiritual loneliness, of man, of that bar which stands between man and his fellows; a bar which, as he says, is the more painfully felt, the nearer the bodily connection.