Stained By Starlight by Sara Ivy Hill

I make the rules. He breaks the rules.

BREE
Life’s a game, and I thought I knew the rules. But the game changed when I was abducted from Earth and sold to an alien pleasure house. New rules? Earn my freedom any way I can.
The fastest route is warming the brutish king’s bed. He’s dominating, possessive, and ruthless with his attentions. He doesn’t just want to claim me as his concubine. He wants to conquer me.
I shouldn’t enjoy that as much as I do.
The more time I spend with him, the more I wonder if I want to be free of him at all.

THREN
My brother has claimed the emperor’s throne—the throne that should have been mine. He’s offered to share his power with me, on one condition: Find and rescue the missing terrakins so they can return to their planet.
I found one. But I have no intention of rescuing her. And I am definitely not returning her.
She’s mine.
My fated queen. My key to power. And possibly my undoing.