The Boy Who Wanted Wings by James Conroyd Martin

Expert archer Aleksy has his heart set on joining the elite hussars at the Battle of Vienna.
Countess Krystyna turns his heart in a different direction.
As an outsider, Aleksy knows that both dreams are forbidden. And yet, one day he finds that he must choose between the two.
-~Romeo and Juliet with a Twist
~~"A pitch-perfect follow-up to his Poland Trilogy"~Historical Novels Review
It is September 11, 1683, and the Ottoman Turks stand at Vienna poised to bring down the weakening citadel and impose jihad. Their sights are set on all of Europe.
Aleksy, a Tatar raised by a Polish peasant family, holds in his heart the wish to become a Polish winged hussar, a Christian lancer who carries into battle a device attached to his back that holds dozens of eagle feathers. As a Tatar and as a peasant, this is an unlikely quest. When he meets Krystyna, the daughter of the noble who owns the land that his parents work, he falls hopelessly in love. But even though she returns his love, race and class differences make this quest as impossible as that of becoming a hussar. Under the most harrowing and unlikely circumstances, one day Aleksy must choose between his dreams.
An IPPY GOLD MEDAL 2017 winner from the Independent Publisher Book Awards
Historical Novels Review
"This classic different-worlds love affair provides the human grounding for a larger story replete with well-researched period details about the struggle of 17th-century Europe against the forces of Islam, and Martin is a skilled enough storyteller to keep the whole narrative moving forward briskly to a very satisfying conclusion. The author has written a pitch-perfect follow-up to his Poland Trilogy."