Yarrow by Crystal Dawn

He’s half witch and half fire demon, although he’s all male. He’s always denied his witch half because his father was bitter about being a witch. That’s why he thought it made him weak, but when his cousin Zorth comes home to visit, he sees the strength he’s found in learning witch’s magic. Zorth doesn’t even have witch’s blood and he’s managed to become everything Yarrow hopes he can. All he needs is someone to teach him.
Zorth has never asked anything of her and she owes him more than one favor, but training a demon? What is he thinking? Wisteria finds the young demon dashing and handsome, but he’s also scary sometimes. Especially when his eyes start to glow and fire leaps from his fingertips. She’ll teach him as a beginner, but once he’s at novice level, Zorth will have to find someone else. Hopefully she can hold on to her heart for that long.