Since We Fell by Ann Gimpel

An idealistic woman.
A naïve man.
A life-shattering mistake.

Juliana is relentless, driven, focused. An archaeologist, she’s clawed her way to the top of the heap. It’s a lonely heap, but the only man she ever loved proved men aren’t worthy of her time.
Discarded by the woman of his dreams midway through college, Brice never offered his heart again. A world-recognized expert on lung diseases, he has his work. Usually it’s enough.

It’s almost Christmas, and Juliana is called home from a dig to see her dying twin one last time. She and Brice are thrown together after a fifteen-year hiatus. She tells herself nothing’s changed, but her heart sings a different song. If she listens to it, there’s only one true love.