Dancing With Death by Catherine Lievens

When a necromancer’s powers spiral out of control, he must choose between trusting his boyfriend’s deadly past or losing him forever to the organization hunting them both.

Cyril thought he understood his necromancy—until his powers began changing in ways that terrify him. They feel stronger and almost out of control, and his beloved pet Oscar is growing more aggressive by the day. But that mystery takes a backseat when people from Vale’s past come with threats instead of questions.
Vale has spent close to ten years trying to forget the Organization and the blood on his hands from his time with them. He should have told Cyril about that part of his past, but how do you explain to the man you love that you had to obey orders you didn’t agree with? Now his former employers want him dead, and they’re willing to destroy anyone who gets in their way.

When Cyril starts experiencing nightmares of other people’s deaths, he’s forced to confront the horrifying possibility that the gentle, protective man he’s fallen for might have killed people he swore he’d never hurt. With his powers spiraling out of control and enemies closing in, Cyril has a choice to make.

And a boyfriend to save.