The Legend of Heart Mountain by K.C. Lynn

Nestled deep in the Canadian Rockies, the scenic town of Passion Falls holds a mountain very few know about. With it comes a legend that states at the stroke of midnight, under the light of a full moon, if you share a kiss on the mountain’s ledge, you will be bound to your one true love forever.
Most people think it’s a bunch of hokey pokey, but not eight-year-old Ellie Mills, she knows it’s true and she’s determined to prove it. What better person to do that with than her best friend, Gunnar. It takes some strong convincing, but he eventually agrees, and the two set off to test one mountain’s magic. Unfortunately, it doesn’t turn out the way Ellie hoped, leaving her heartbroken.
Now, seventeen years later, Ellie has another plan to rope Gunnar into, this one even crazier than the last. Once again, he will give Ellie what she wants, but this time, they’re going to play by his rules, and it will forever alter their friendship.

But maybe that’s how it was always supposed to be. Maybe Ellie was right and the legend of Heart Mountain isn’t just a myth after all.