Jem is not really upset at all at the end of Chapter Ten. Rather, he is somewhat in awe of his father, who he has just witnessed kill a rabid dog in the streets of Maycomb with a single shot from a rifle. In fact, he learns from Miss Maudie that Atticus was once known as "One-Shot Finch," the best shot with a rifle in the county. He does make it clear to Scout that...
Jem is not really upset at all at the end of Chapter Ten. Rather, he is somewhat in awe of his father, who he has just witnessed kill a rabid dog in the streets of Maycomb with a single shot from a rifle. In fact, he learns from Miss Maudie that Atticus was once known as "One-Shot Finch," the best shot with a rifle in the county. He does make it clear to Scout that he doesn't want her to tell her schoolmates about the encounter with the dog, or about what a crack shot her father is (he correctly realizes that Atticus would regard that as vain and overly proud) but he is hardly upset. Indeed, at the end of the chapter, he exclaims that Atticus is a gentleman, just like him. It is possible, though, that you are referring to the end of Chapter Eleven, when Jem is overcome with complex emotions after the death of Mrs. Dubose, an old shut-in and, it is revealed, a recovering morphine addict. Atticus had for weeks ordered Jem to visit and read books to the old lady, who never failed to make him angry by calling Atticus a "n----r lover" in addition to a number of insults directed at him. When she dies, Jem's response is emotional.