The Darkest Oath by Lauren Lee Merewether

Her love is his only salvation—and the undoing of everything he needed to survive.
An immortal knight. A fearless rebel. A love forged in the fires of revolutionary France.

Chevalier Rollant de Montvieux was once a man of honor. Betrayed on the battlefield and bound by a sorceress’s curse, he has spent six centuries serving the French crown—immortal, untouchable, and doomed to lose anyone he dares to embrace in love.
As revolution smolders in the streets of Paris, Rollant clings to duty as his only purpose in a wretched existence, until he meets her.
Élise has nothing left to lose. Defiant, outspoken, and determined to fight for freedom, she has no patience for kings or the royalists who serve them. But when she crosses paths with Rollant in a spy’s disguise, she senses something different beneath his quiet strength: a man burdened by secrets, trapped in a fate not of his choosing.

Drawn together by forces neither can control, their connection deepens in the shadows of a crumbling world.
But Rollant knows love is forbidden to him.
To hold Élise is to curse her to certain death.
As France teeters on the edge of war, Rollant must make an impossible choice: honor his unbreakable oath and protect her from afar—or risk everything, including her life, for one fleeting chance at love.

And Élise must decide where her true battle lies: in the streets of Paris, or in the arms of a man who may be her ruin—or her greatest salvation.