The Ones Who Undid Tomorrow by Katherine MacDonald

Selene defied fate once. She fell through time, seized a new life, and found unexpected love in a marriage that was never meant to be more than convenience. Together with Dorian, she altered history itself. But just as their hard-won peace begins to feel real, Selene learns a chilling truth—she was not the only one to fall.
Dorian has spent his life guarding secrets. Loving Selene was never part of the plan, and yet he would do anything to protect her. But the past he tried to bury is stirring again. And something—or someone—is pulling the strings from the shadows, manipulating Duke Drakefell and threatening to unravel everything they’ve built.
War brews on the horizon. As old enemies resurface and darker powers close in, Selene and Dorian must confront the truth: the battle they thought was won has only just begun. To save their love, their country, and the future they’ve forged, they must face a force that has always been one step ahead.
Because fate is not a thread to cut.
It is a hand—and someone is still holding the scissors.