Tax time.

Hi mummas.
So this is my first year being a defacto relationship and tax time. My partner believes that doesnt have to lodge a tax as a defacto. Just as a single man. So is that possible? Or will he have to do one as defacto? Also do I have to do the same? Centerlink is aware we are together etc. Just unsure about tax time. I am going to see an accountant to do tax, just want to be prepared when he calls me in flap asking what my income was incase he does have to do one.