What has Miranda not noticed about Sal's behavior lately that might indicate that he wanted to withdraw from her for awhile?

Miranda also tells the reader, as well as the mystery note writer, how Sal got punched on the way home from school one October afternoon. This seems to have been the catalyst that has caused Miranda and Sal to stop being friends, but the reader should note that Miranda had to rush to catch up with Sal that day and it was not the first time he began walking home without her.