Watcher by Charity Parkerson

Two outcasts in the world. One is completely insane, while the other is a cold-blooded killer. Some days it’s impossible to know which is which.
By day, Atticus is CEO of a major tech company. At night, he enjoys a darker lifestyle. His life is filled with secrets. Every space is his playground. The doors his money and looks won’t open are thrown wide for his twisted reputation. While Atticus can’t claim he has gotten everything he ever wanted, he fully intends to own Foster.
Despite Foster being part of an organization of hired killers, he leans toward a quiet life. His position with Killers Inc. doesn’t require working closely with anyone. Maybe that’s why he’s never fit in, even with his so-called family. His loner status is more likely due to him not trying to connect. Now there’s this guy who won’t stop pestering him. Foster might have to kill his annoying ass. That is, if he can stop watching him.