Upon his arrival each summer in Maycomb, Dill Harris becomes an immediate playmate of Jem and Scout, who seem to have no other close friends in To Kill a Mockingbird. While Dill's appearance divides Jem and Scout somewhat, he manages to walk freely in both of the Finch children's worlds. He becomes a much-needed male companion for Jem, and they often exclude Scout on some of their excursions, most memorably their skinny-dipping trip to Barker's Eddy. Dill coaxes both Jem and Dill into forays to the Radley House in the hopes of getting a glimpse of Boo, of which Dill has become obsessed. Dill also becomes Scout's first love interest, and she anxiously awaits his arrival each summer. Dill writes her love letters, and he promises to marry her one day. They share kisses (when Jem is not around) and spend an innocent night together in Scout's bed, discussing their parents, babies, Boo Radley and
Beautiful things (that) floated around in his dreamy head.
Scout and Jem were very close, always playing together. However, Dill is the male companion that Jem needs. Hanging out with another boy shows Jem that he doesn't want to be hanging out with his little sister anymore. It shouldn't be blamed completely on Dill, though. Maturity also plays a part. Jem is beginning to go through puberty and is changing around the time Dill comes along. The forces together work to distance Jem from Scout and change their relationship.