I have 3 wires coming into a single light switch box. One is from the breaker, one goes to the fan (includes light), and I believe the other wire goes to the next switch in the circuit. The single switch currently turns the fan and light. There are no other switches in this room that control fan and light.
The wiring looks like below. I'm trying to replace the single light switch and install a Decora dual switch so I can control fan and light separately with existing wiring. Is it possible? If not, can I add a new switch altogether (cutout the single gangbox and install a two gangbox) with the existing wires so I can have separate switches for fan and light? I'm trying to avoid running a new wire.