Red Hook Road by Ayelet Waldman
Waldman (Love and Other Impossible Pursuits) follows the aftermath of two families after a young couple dies in a car crash an hour after their wedding. 
Why it’s a great summer read: Because it’s the summer! Wedding season! And car crash season! And long ruminations about the way death initially unites us but also infuses all of our interactions with sublimated, unending residual pain until we finally come to an understanding of ourselves and each other season!