The Stars Undying by Emery Robin

A "dazzling" tale of empire and betrayal set among the stars (#1 New York Times bestselling author Casey McQuiston), this queer, spectacular space opera draws inspiration from Roman and Egyptian empires—and the lives and loves of Cleopatra and Julius Caesar.
Princess Altagracia has lost everything. After a bloody civil war, her twin sister has claimed both the crown of their planet, Szayet, and the Pearl of its prophecy: a computer that contains the immortal soul of Szayet's god.
So when the interstellar Empire of Ceiao turns its conquering eye toward Szayet, Gracia sees an opportunity. To regain her planet, Gracia places herself in the hands of the empire and its dangerous commander, Matheus Ceirran.
But winning over Matheus, to say nothing of his mercurial and compelling captain Anita, is no easy feat. And in trying to secure her planet's sovereignty and future, Gracia will find herself torn between Matheus's ambitions, Anita's unpredictable desires, and the demands of the Pearl that whispers in her ear.
For Szayet's sake and her own, she will need to become more than a princess with a silver tongue. She will have to become a queen as history has never seen before.
"A glittering triumph of a book that weaves together history and tragedy into a star-spanning epic." —Everina Maxwell, author of Winter's Orbit