Rothana - Star-Fae Duology, #2

A new queen falls. A death lord rises. An ancient foe looms in the shadows. Sylvie Imanthiya is desperate to lead Faerie well and deepen her bond with her husband, former king Taylan Ashkalabek. But all hope of that vanishes when the winter solstice ceremony ends in disaster, stranding her and Taylan in the Deathrealm, and stripping the kingdom from her. With Faerie in chaos, Zad and Diza are separated once again: Zad to reconcile with an old mentor and stabilize the kingdom, and Diza to confront the nefarious Casimir in the mortal realm.
But Casimir claims that a greater evil seeks to destroy both realms, an evil that Diza's unique power can hold at bay-if she could only remember how. In the Deathrealm, Taylan is succumbing to the lure of specters from his past, and pushing away Sylvie's love. Overwhelmed by decay and darkness, Sylvie must summon unexpected magic from the soul of Kyure to fight for her convictions and her husband's heart.
Shadows divide them. Their friends are in peril. If Sylvie fails, her marriage and her world will fall.