In Breathing Underwater, what reason does Tom give Nick for not giving him a second chance?

At the beginning of the story, Nick is found guilty of beating up his girlfriend, Caitlin. After this, his best friend for about ten years, Tom, refuses to speak to him. Nick and Tom had been best friends "since first grade," which is when Nick figured out that "Tom's peaceful house was the best place to escape (his) father."
Nick asks Tom to give him a second chance, saying, "You'd think your best friend would give you a second chance." Tom says in reply, "I don't even know who you are . . . My best friend . . . wouldn't do what you did." In other words, Tom refuses to give Nick a second chance because he simply does not want to be friends with someone who could, and did, beat up his girlfriend. Tom's refusal may also be influenced by the fact that, during the trial, Nick initially denied having beaten up Caitlin, making the process for her all the more painful.
Nick thinks that Tom, "who knew (him) better than anyone . . . should have stood by (him)." However, after Tom refuses to give Nick a second chance, Nick says that he "was stupid thinking (he) could work things out with Tom," and he acknowledges that he is now on his own.