Dream State by Eric Puchner

Cece is in love. She has arrived early at her in-laws' beautiful lake house in Salish, Montana, to finish planning her wedding to Charlie, a cardiac anaesthesiologist with a brilliant future. When Charlie asks Garrett, his best friend from college, to officiate the ceremony, Cece can't imagine anyone less appropriate for the task.

After all, Garrett, a depressed baggage handler at the local airport, doesn't believe in marriage. But as she spends time with him and his gruff mask slips, she grows increasingly uncertain about her future, leading to an impulsive decision that will alter the three friends' lives forever - the events of that summer reverberating across fifty years and spanning generations.