"Twenty Boy Summer" by Sarah Ockler is technically a "young adult" book, but it is enjoyed by adults, I am proof because I am one, and I enjoyed it immensely, so forget stupid categories on this one people. (Unless you are a young adult, then you are set).
Here's the deal, Anna and Frankie are best friends, what Frankie doesn't know is that Anna is in love with Frankie's older brother Matt. The two keep their relationship a secret, and the three's worlds turn upside down when they get into a car accident, and the only survivors are Anna and Frankie. A year later, with hearts still fragile, the girls go on a fabulous summer vacation to California.
Secrets, death and heartache. Doesn't seem like a typical summer read that you would want to enjoy, but you will find it insightful and youthful. Self discovery is something that we can all relate too, and friendship is friendship, no matter how old you are.