Any idea what happened here?

I was ahead in life and he fatigued both of us to death, he drew first and died before I did but I still lost. I'm just assuming since it was his turn and he caused the lethal damage that it gave me a loss or did we both lose?

I'm pretty sure when you both die you both lose unfortunately.

Everything resolves before the game ends. At the end of the effect neither of you were alive. If you both die its a draw and it shows a defeat screen for both players.