This character is always a figurative "girl next door" type, and sometimes, as with the ladies of Dawson's Creek and The O.C.'s Marissa (Mischa Barton), they literally live next door.
The young actress who plays this stock character has quite a burden on her shoulders. She has to give hope to young men across the country who feel they've been "friend-zoned," while saying the right things to always embody that paragon of perfection who grew up one lawn over.
If the main character is a girl, then, yes, expect the "guy next door." Regardless of their gender, this archetype always exemplifies adolescent wish fulfillment. It'll take a season or two before they seem like actual flesh-and-blood characters.