Hopeless question

I've been looking for this book that is somewhat similar to hopeless; but can't for the life of me remember the title or author! main character is Lee (or Emilee) and she has an ex from highschool that one day just up and disappeared, named Reiner. One night she sees Reiner in a nightclub but is surprised that he doesn't know or remember her. If anyone has any idea what this book is or anything please please PLEASE let me know! Thank you!