Daybreak by Matt Gallagher

A disillusioned American veteran volunteers for the war in Ukraine to reconnect with a woman from his past in this timely and powerful novel from a "vital" (The Washington Post) voice in contemporary literature.
Thirty-three-year-old Luke "Pax" Paxton has been out of the US military for almost a decade, adrift in an America he no longer understands, haunted by a mistake made in an unforgiving moment of combat. When an old army friend suggests they travel to Ukraine to help fight against the Russian invasion, he agrees, and together they cross an ocean to Lviv, the City of Lions. But Pax isn't merely going out of the goodness of his heart. He carries with him the address of a former love, a Ukrainian woman named Svitlana whom he had known as a young soldier and has been unable to forget.

His feverish journey through Lviv takes him down winding and missile-cratered streets as he forms surprising connections with everyone from humanitarian volunteers to displaced Ukrainians and ordinary citizens trying to survive. And when Pax gets the chance to save someone dear to Svitlana, he just might be able to correct the wrongs that have wracked him with guilt for so many years.

Inspired by the author's time in Ukraine, Daybreak is a deeply moving love story, as well as an exploration of the struggle to find meaning and redemption in the midst of war.