28 summers / Elin Hilderbrand.

Enhanced descriptions from Syndetics:

A "captivating and bittersweet" novel by the #1 New York Times bestselling author of Summer of '69 : Their secret love affair has lasted for decades--but this could be the summer that changes everything ( People ). When Mallory Blessing's son, Link, receives deathbed instructions from his mother to call a number on a slip of paper in her desk drawer, he's not sure what to expect. But he certainly does not expect Jake McCloud to answer. It's the late spring of 2020 and Jake's wife, Ursula DeGournsey, is the frontrunner in the upcoming Presidential election. There must be a mistake, Link thinks. How do Mallory and Jake know each other? Flash back to the sweet summer of 1993: Mallory has just inherited a beachfront cottage on Nantucket from her aunt, and she agrees to host her brother's bachelor party. Cooper's friend from college, Jake McCloud, attends, and Jake and Mallory form a bond that will persevere--through marriage, children, and Ursula's stratospheric political rise--until Mallory learns she's dying. Based on the classic film Same Time Next Year (which Mallory and Jake watch every summer), 28 Summers explores the agony and romance of a one-weekend-per-year affair and the dramatic ways this relationship complicates and enriches their lives, and the lives of the people they love.