The Abyss by Lily Archer

Beth has lured me into the slave rebellion with promises that spark a fire in my heart … and in other places, as well. The Bazaar will either lead to a revolution, or end in countless lives lost and an even greater stronghold for slavery. On top of that, an old enemy has arisen, and fighting him will take every bit of strength and magic I possess. But he has more lives and more plans than I can fathom, and each of them includes destroying the realms, my king, and my mate.
Beth’s journey to the mines is even more fraught with danger, but her will is insurmountable, and my need to claim her only reinforces our agreement. The future may be filled with pitfalls, but I swear to the Ancestors I will get her to the mines and claim her so well that she will never doubt my devotion. But first, we’ll have to survive the deepest, darkest hole in all of Arin–the Abyss.