Dragons and Mayhem by Poppy Wolfe

Arawn, Duke Tiamat, absolutely, positively, definitely isn’t falling into a mating fever, and that’s the problem. A year ago, Arawn met the most bewitching woman, Willow Sage, and they hit it off. Within six months, they’d moved in together.
And six months after that, Arawn still was showing no signs of mating fever.
He didn’t tell her he was a dragon shifter, of course. Natural people have such strong reactions to learning about the hidden supernatural world, so supernatural people don’t admit anything unless they’re engaged.
And they weren’t engaged because, obviously, Willow wasn’t Arawn’s fated mate.
So, on the advice of everyone, Arawn broke it off and broke both their hearts. His fated mate was waiting for him somewhere, and when she walked into his life, he would be helpless to resist the mating fever anyway.
But now, Arawn has been blackmailed into returning to Las Vegas to take over the soft opening of the Dragon’s Den Casino. When he walks into the Human Resources division to meet the new witch who’s going to take care of the sickly sea serpents in the fountain out in front of the casino, it’s Willow Sage.
Willow Sage, the love of his life but not his fated mate, and she’s a witch.
They try to work together to care for the sickly serpents, but their attraction and lingering love is just too strong. Within hours, he wants to spend time with her. Within weeks, he’s hopelessly in love with her again.
But he isn’t falling into mating fever.