Lord of Embers by C.N. Crawford (The Demon Queen Trials #2)

Once, I was a broke college student. Now, it seems I'm destined to rule as the Lightbringer--queen of the demon realm. Except I have competition in the form of Orion, the Lord of Chaos. Like me, he has been marked as a leader. We can't keep our hands off each other, even if he swore an oath to kill me.

It seems we both want the same thing--the crown. And in this battle of wills, only one of us will be left standing.