Holden goes to the Antolini's because he basically has nowhere to go. He has gone home to talk to Phoebe and left and lacks the money to continue to stay at the hotel, etc. Mr. Antolini was a favorite teacher of his so he decides to look him up and takes a cab to his house.
Mr. Antolini welcomes him excitedly and they discuss a number of things and Mr. Antolini tries to convince him that he should get an education and that it is important.
Once he sees that Holden is tired, he gets things ready and puts him to bed and Holden falls asleep. But when Holden wakes up and Mr. Antolini has his hand on his head, he is terrified a this show of affection and bolts.
He claims that he is acting in a perverted way and comes up with all kinds of justifications but his fear of connection and affection are what drive him away.