Apartment using ground wire as neutral
OK, disconnect that pendant light until you fix the problem. you can't have a ground wire carrying load. There is no neutral in that box.

You've got to choices (well, maybe more), you can run a new feed to the duplex switch and utilize the unused white and red wires to get neutral and switched power to the pendant light after disconnecting the switch from the existing source. You could also run a new feed to the pendant light box, connect neutral to light and utilize the black and red wires for switched hot after disconnecting switch from existing source. 

Remember to connect all grounds from new feeds to existing ground wires