One True Loves by Taylor Jenkins Reid

Emma marries her high school sweetheart Jeese, but on their first wedding anniversary, he goes missing in a helicopter crash. He is presumed dead, so Emma must move on. A few years in the future, she has reconnected with her high school acquaintance Sam, and has made a new life for herself. Just months away from her and Sam's wedding, she gets a call that Jesse is still alive and is coming back to her.

One Day in December by Josie Silver

Laurie is on the bus home from a long day at work when she meets eyes with a man on the street. It is only for a few seconds, but it makes an impression on her. She spends the whole next year trying to find her mysterious bus boy, only to finally meet him when her best friend Sarah introduces him as her new boyfriend. From there, Laurie, Sarah, and Jack are woven into each other's lives.