Fae World by Eve A. Hunt

I always thought if I had magical powers, life would be cake.
Wrong.
My fated mate is the enemy of my kind, I have days to figure out how to keep him from literally going up in smoke, and at any moment one of my magic’s surges will shock my heart and strike me down.
If I don’t learn how to control my mage abilities pronto, I’m dead. I thought that portalling to hang with other mages would solve things, and I’d find some rad crone-like chick to help me train all epic style. But it seems I’ve landed myself, my best friend, and my doomed fated mate in a hidden kingdom where my kind are enslaved for eternity. Not awesome.
This is not the training I was hoping for. And with every day we’re away from the cursed castle, Lucus and his brothers weaken further. If I don’t get us the heck out of this super creepy British fae kingdom, all of us—the 16th century guys and us modern gals—are history.