Holden seems to be reaching out for genuine intimacy in his encounters. Is he himself capable of intimacy, and are any of the other characters capable of providing it? What is intimacy?

One can argue that there are several characters in Holden's life that seem capable of providing genuine intimacy and affection for him throughout the novel. Holden's history teacher, Mr. Spencer, seems like he is genuinely concerned with Holden's life and takes time out of his day to offer Holden words of advice and encouragement. Mr. Antolini is another adult who is concerned about Holden's well-being. Unfortunately, Holden wakes up to find Mr. Antolini admiring him and leaves his apartment immediately. Holden speaks highly of Jane Gallagher and is infatuated with her throughout the novel. Holden also mentions that he used to get along really well with D.B. until he became a screenwriter. Out of all of the characters that display affection for Holden and are genuinely concerned about his well-being, the only person Holden relates to is Phoebe. Unlike Mr. Spencer, Mr. Antolini, and D.B., Phoebe is a child, who shares Holden's perspective of the world.
Despite Holden's "attempts" to find intimacy, one can argue that he is not capable of accepting affection from others. Holden is a traumatized, jaded, hypercritical adolescent, who is experiencing a mental breakdown. While there are people in Holden's life willing to help him, Holden continually rejects their affection in favor of searching for intimacy and love from strangers. For example, instead of calling Jane Gallagher, a girl who knows Holden on an intimate level, Holden chooses to call Carl Luce, Faith Cavendish, and go on a date with Sally Hayes. Holden's inability to accept love from people he genuinely cares about can be interpreted as a way to protect his emotions. This could stem from the tragic death of Allie. In order to avoid being hurt again, Holden isolates himself and rejects advice and affection from others, which only exacerbates his crisis.