Opie develops a crush on his teacher, Miss Crump ("Opie Loves Helen," Episode #132). Of course, he's not the only Taylor man with an interest in Helen. Andy must find an appropriate way to explain to Opie that Helen is his girl, no Opie's.
Opie takes the news just fine. As long as Helen is someday part of the family, Opie explains, "I don't care whether she's my wife or my mother."