This is *One True Loves by Taylor Jenkins Reid* - from the author of _Daisy Jones & The Six_ and _The Seven Husbands of Evelyn Hugo_.
Published *2016*. Now also a movie starring Phillipa Soo, Simu Liu and Luke Bracey.
Here is a summary in English:
*Emma Blair thought she only gets one true love in a lifetime.*
At *17*, in her small town of Acton, Massachusetts, Emma knows she will marry her high school sweetheart *Jesse Lerner*. He is adventurous, charismatic, free-spirited.
In her *20s*, they do marry. They move to Los Angeles, build a life far from their parents. Emma works as a freelance writer, Jesse works in a travel magazine. They travel the world together - they live for adventure.
On their *first wedding anniversary*, Jesse is on a helicopter over the Pacific Ocean near Alaska for work. The helicopter goes missing. No wreckage is found. He is presumed dead.