sneaky link
secretive
the one-line answer
A secret romantic partner kept hidden from others.
Sneaky link means the person you are seeing that nobody knows about. Not a girlfriend. Not a boyfriend. Just someone you see quietly.
mainstream
Your coworker might use this word.
01 / in the wild
hear it move.
description
he has a sneaky link. nobody knows who she is.
He has a secret romantic partner that he keeps hidden from everyone.