Ghostmate
A roommate who is never at home. Pops in every now and then and grabs some of their shit, and then disappear again for an undetermined amount of time. You might also hear random noises in your house when you think you're alone, much like a ghost, but it is in fact a rare appearance by your ghostmate.
Jim: How come whenever I come over, Mike isn't home?
Adam: because he's a ghostmate. He only pops in every now and again, and each time he does, it spooks the hell out of me.
Adam: because he's a ghostmate. He only pops in every now and again, and each time he does, it spooks the hell out of me.