Leather & Lark :- The Ruinous Love Trilogy ( Book 1 ) by Brynne Weaver

And they can’t stand each other.

Indie singer-songwriter Lark is the sunshine and glitter that burns through every cloud and clings to every crevice that Lachlan Kane tries to hide inside. The surly older brother of her best friend’s soulmate, Lachlan thinks she’s just a privileged princess, but Lark has plenty of secrets hiding in the shadows of her bright light. With her formidable family in a tailspin and her best friend’s happiness on the line, she’s willing to make a vow to the man she’s determined to hate, no matter how tempting the broody assassin might be.

As Lachlan and Lark navigate the dark world that binds them together, it becomes impossible to discern their fake marriage from a real one. But it’s not just familiar dangers that haunt them.
There’s another phantom lurking on their doorstep.

And this one has come for blood.