Dakota Lightning by Dawn McClure

Stuck in the friend-zone circa 2004.
Abby Spencer is head-over-boots in love with her best friend, and he doesn’t have a clue—that is until his twin sister spills the beans, throwing Abby into a tailspin of denial and tough choices. Should she move on and start dating the new hot guy in town, or fight for the only man she’s ever loved and pray he’ll eventually see her as more than a friend?

Three can keep a secret…if two of them are dead.
Matthew Evans never had a clue that his best friend had feelings for him. Truth be told, he thought of her more as a sister than a friend. He’s also never kept a secret from her, but when her father suddenly decides to sell the Spencer Ranch to the Evans, Matt promises not to tell Abby until her father finds the right time to break it to her himself. With their friendship finally developing into something more, will the secret tear them apart?