The boy next door is an archetype of storytelling. He is often invoked in Western contexts to indicate wholesome, unassuming, or "average" masculinity. He is a young man with a sweet, shy demeanor who is just discovering his physical and spiritual strengths and her lives next door. The boy next door maintains his innocent wonder due to his charm, sincerity and preservation of virginity. He is never arrogant. The boy next door may have a sidekick, who shows somewhat less promise than the boy next door; this will serve to heighten his appeal by contrast.
A boy next door may serve as a love interest for a female protagonist. In this case, he is most likely someone the protagonist has known for most of her life, but in the past couldn't appreciate because of her age. As a love interest, the boy next door is always physically close, yet at the same time detached from the protagonist. He is the sweet boy the protagonist sees everyday, a really great friend, or the perfect boy to bring home to her parents.