Eyes on me (Ghost x reader)

Everyone in the department knows you, one of their greatest detectives, has become obsessed with the Ghost case. You don't sleep much anymore, don't go home unless you have to and don't know when to stop chasing the man behind the skull mask.

Ghost, meanwhile, has grown just as fixated on the anonymous detective who's always one step behind him. He has no face nor name from them, only their badge number and the infuriating habit of theirs to almost catch him.

Then, by pure chance while trying to investigate a fresh crime scene Ghost left behind, you meet Simon Riley. He's charming enough, quiet enough and honestly really hot. You two fall in love and start dating without ever talking about your jobs.
After all, Simon doesn't know his girlfriend is the detective hunting him and she has no idea she's sleeping with the man she's been trying to catch for months.

Or:
Two obsessed stalkers date each other without knowing they're each other's object of obsession, playing a game of cat and mouse.