Promise We Made at My Favorite Sandbox

Raspberry is a seventeen year old girl who has isolated herself from any other boy because of a promise she made with her first crush (Seth), but when she meets a mysterious boy (Leo) at the park and claims to know her and kisses her, she slowly grows closer to him. How does she know Leo, and why can't she remember but he can? Will Seth ever come back for her, or will Leo sweep her off her feet?