Forged in Fire by Rachel Langella

For three hundred years, Harlan Edgewood’s monthly shifts have been agonizing. Then he meets Whimsy Hickes—a mage who specializes in transformation—and the attraction is both immediate and mutual. But Harlan takes refuge in denial, believing his curse is too great a burden to inflict on any lover.
But Whimsy knows he can help.
When Harlan is provoked into an unexpected transformation, Whimsy uses his magic to ease Harlan’s pain, but with an unexpected consequence. While he’s shifted, Harlan’s wolf recognizes Whimsy as his mate.
Yet even as they try to figure out their relationship given Harlan’s doubts, suspicious events in the Asheville magical community escalate. Shifters are disappearing, others are murdered, and Harlan’s curse makes him an obvious target. It will take all of Whimsy’s magic to drive back the rising evil—and if he fails, Harlan will lose not only his life, but his very soul.