Jem's Sensitivity

Jem was crying because Nathan Radley had filled the knothole up with cement. The knot hole was Boo's connection to the world and with the hole plugged Boo cannot attempt to make a friendship. The reason why Jem is sensitive now is because he is maturing. Jem feels sad about him because he realizes his deep loneliness. Scout and Dill still have bad feelings about him.