The Fireblade Array, book 1: City of blaze
H.O. Charles2014

The city is crumbling beneath a mountain of its own indulgences. Its army abuse the castle's servants, confident that deadly wielders have been exterminated; wars are fought to encourage otherwise absent mortality; countless people suffer from the terrible pangs of nalka, the hunger for intimacy; and all the while its king concerns himself with choosing which of his disappointing concubines to execute next. The duty falls upon his emotionally withdrawn son, Morghiad, to restore the city's strength and the army's purpose. In his attempts to do so, he uncovers darker horrors and encounters a young servant who could either be his greatest ally or his greatest hindrance.