Summer Lightning (Vintage Paperback) by Wendy Corsi Staub

Love you to death... 

Melissa Loring knew that she was a lucky girl. She had everything she’d ever dared ask for, including the love of Tripp, a handsome, devoted boyfriend. But somehow, Melissa wanted more. She’d always had the magical feeling that someone was watching over her, and she dreamed of meeting an earthly love who could make her feel the same way.

Then on Melissa’s seventeenth birthday, her dream came true—almost. Schuyler Whitfield revealed himself as her invisible protector—and a ghost. And he offered her his love.

Now Melissa must decide whether to accept the love of a specter or to hold on to her real-life love with Tripp. But can an ordinary guy ever compete with the seductive power of the unknown?