Long Live the Elf Queen by J.M. Kearl

Layala fought against falling in love with him. Thane battled to win his mate’s heart. Now they’ll discover if their love can withstand those who tore them apart.
Held for weeks without food or water, Layala’s resolve begins to fracture as an evil darkness looms over her. She’s the key to destroying the Void or reviving its creator— the long-dead Black Mage she has a mysterious connection to. Her adversaries will do anything and kill anyone to make the latter happen.
Layala and Thane learn what it truly means to fight for love as their enemies surround them and it becomes a struggle for revenge, the kingdom, and finding the truth about why Layala seems to harbor the power of whether Palenor falls into darkness or if her Lightbringer name holds true.