Dark Heart by Eve L. Mitchell

Nice guys finish last. It’s a motto I live by. In my world, it pays to be the bad guy—and I’m very good at being bad. I have a thriving business built on blood, sweat and tears—literally. Illegal fights are my bread and butter, and no one interferes with that. Including an expensive-looking, blue-eyed blonde with a mouth that just won’t quit.
Babysitting Lela Morgan starts out as a favour to a “friend,” but quickly becomes more despite my cruel words and her bad attitude. But if there’s one thing I cannot afford to become in this world, it is soft. So I will fight against her charms. I will fight against her bratty behaviour and the way she pushes all my buttons.
As our relationship grows, I realise I’m in danger of losing control—and that’s never happened before. Ever. When all hell breaks loose will my bad guy rep still be intact? And more importantly, will my heart?

*This is an Enemies to Lovers, New Adult Romance.