Fate Has No Name by Dan Barker

A government employee has his life changed when he becomes infatuated with a college girl. Using any illegal means necessary, he finds out whatever he can about her, all without making sure she never even knows he exists. However, the more he discovers, the more he realizes things are not what they seem and he becomes obsessed with protecting her from dangers of which she was not aware. It's not love, it's fate.