Yep. When the sensor fails you get --.-- readings. It's unlikely the fuel killed it -- even if it had a lot of ethanol in it -- they just fail after a while, especially if running rich.
You probably need this part (search around -- you'll find a Bosch or Denso that will fit but may be cheaper
Universal EMS Wideband UEGO Sensor Kit
Check your model to ensure right p/n....