The Time Keeper - The Guardians of Time, #1

Undemanding and beautiful in an understated way, Emilia Delcourt is the perfect girlfriend for Justin, high school football hero and all around golden boy. With plans to go to Stanford University after graduation, the future is golden. except everything is not quite as perfect as it seems. Behind her quiet, submissive front is another Emilia - daring, feisty and craving adventure. And that girl is itching to break free.
When Emilia finds out she's from a long line of time travellers destined to save the world, it just might be time to find out who the real Emilia is. Sebastian Gates is ex-Army, smoking hot and able to do some pretty wicked magic. He has it all. except he doesn't. Haunted by a painful past, he's a loner and that's the way he likes it. So when he's partnered up with Emilia to travel back in time, he's furious...
to put it lightly! He's always made a point to keep Emilia at a careful distance and that's the way it's going to stay. The only problem is, with no expectations on her, Seb is the one person who brings out the real Emilia and she's determined to find out what makes this brooding, enigmatic guy tick. Thrust into Regency England and WWII Paris, they have to find a way to work together and trust each other.
Surely, it's only a matter of time before Seb's walls begin to crumble.