Sally - A book with a character who loves someone so much and actually gets them in the end
Jack - A book with a character who longs for more
Zero - A book with a loyal sidekick
Oogie Boogie - A book with one hell of a wicked villain
Halloween Town - A book that's creepy or has a scary theme
Christmas Town - A book that left you feeling warm and fuzzy inside
What's This? - A book that took you by surprise
The Twilight Series definitely fits the bill. After four books together Edward and Bella's love is still going strong and they actually end up together!
Raven from Vampire Kisses definitely longs for more.
While Valkyrie eventually becomes more independent and not really as much of a sidekick, I'd say she's more of a sidekick in the first Skulduggery Pleasant book, and very loyal.
The villain in The Heartless City is pretty wicked.
Asylum has got some creepy themes for sure.
The romance in Shiver definitely gave off a warm and fuzzy feeling.