Sleeping on his tummy.

So I am laying in bed reading some post and my 2 month old rolls over on his tummy for sleeping. I have been hyper aware of his movement since birth because most nights he sleeps in bed with us. Do I roll him bac on his back or just leave him on his tummy? I hear babies sleep better on their tummy. I am hoping he is getting ready to sleep through the night since I am going back to work soon.