Frost and Desire. Sorcery and Desire

Frost, master sorcerer, wanted an apprentice: someone who would perform the tedious parts of sorcery, while Frost enjoyed the more sophisticated and varied aspects. Sorcery-bound individuals are vanishingly rare, so when he stumbled upon one who'd been overlooked by testers, he counted himself lucky indeed. No matter if the boy was old to begin an apprenticeship; he would learn. After growing up a bastard and a whipping boy, the promise of a future as a rare powerful sorcerer seemed impossible to Thistle.
He braced himself for failure and disappointment. But nothing could prepare him for his growing attraction to his master. And it turns out there is one thing worse than an unrequited infatuation with one's mentor:Having it reciprocated. Content Notes: This novel is an M/M romance with a happily-ever-after. It depicts a relationship that begins as healthy and platonic but eventually becomes abusive.
Ultimately, after a long separation and a lot of consideration, the characters work their way to their HEA. This is a fantasy. It is not intended to suggest that real-world abusive relationships should be "worked on" until they become healthy ones, or that teacher-pupil romances are a good idea (they are not even a good idea in the story). Novel contains an incident of mind-control, nonconsensual sex transformation, and rape.
Also contains explicit sex and consensual bondage. It is not erotica; sex scenes comprise very little of the book.