Rubius’ Throne by Haley Weir

Aeron seems happy and content, at least on the outside.
On the inside, he still burns with rage towards Rubius. He pines over his unrequited love and unmet needs with Cassandra — until Samar shows up at his castle doors claiming to be a human woman fleeing persecution.
When Aeron finds out that she is much more than merely a human, feelings he thought had been lost to him begin to rekindle.
Unfortunately, Samar wasn’t just fleeing — she was being hunted.
Before he can do anything to stop it, the Kingdom of Grenvich is thrust into a war.
Torn between protecting his family from Rubius and protecting the woman he feels strangely drawn to, Aeron winds up in the desperate situation of losing one of the women he cares about and finding an eternally fated love with the other.
To make matters worse, the process might cost him his own life.