Immortal Secrets by L.A. McGinnis

A vicious curse.
A fate that traps them all.
Every ten years, Lady Nyx Corvanus looks forward to only one thing—revenge.
A chance to kill the immortal Lord of Shadows, while submitting to his every whim during breeding night. She’s failed three times, but this time she’s determined to end this nightmare, once and for all.
Darius saw his mate only once—for a brief second, before he was locked in the dungeons to rot. For thirty years he’s been tortured by the merciless High Lord because Nyx rightfully belongs to him.
But one fateful night changes everything, and now they’re on the run, forced to rely on the treacherous Ronan to survive.
Breaking the curse is the last thing on Nyx’s mind as she turns to the two males who rescued her. She’s ready to give Darius her heart, but Ronan might just carve it out of her chest before he’s done with her.