Heart of the shadow king by Sylvia Mercedes

Vor and Faraine return to Mythanar to find their world on the brink of collapse. Though Faraine longs to support Vor in protecting his kingdom, she fights the weakness in her body at every turn – not to mention the strange changes warping her gods-gift. Torn between honour and desire, Vor must choose between his kingdom or his queen. Meanwhile, Faraine risks unleashing a disastrous darkness in herself to prevent a cataclysm.