White = Qe6. Black = Kh8 Qe4 Rf7 g7 h7. I played Qe8+ 
That way, after checkmating him, you can pick off his R at f7.
You must have thought your Q at e6 was blocking his Q at e4 from capturing your Q at e8.
Actually, that was a pretty decent move. After he takes your Q you have no legal moves, stalemate.
Where was the white K?
Bill Smythe
I had this position in July.
I figured I needed my king to mate, so I played …Qg6 and offered a draw.
Alex Relyea
I wonder what kind of rating a computer would give those moves in either of these positions?
Ouch. I twice missed mates in one against 2300+ players – but fortunately one of those had sufficient time pressure that it was almost justified. The worst part is I scored .5 out of those two games.
White King was on g1. Black’s last move was RxN on f7 defending smothered mate) I saw Qe8+ followed by Qxf8#. I presume everyone sees white’s mate in 3 in the shown position. Correct? 
Pretty typical “sight” mistake that can happen when one is in time pressure or not. Get over it and move on. Don’t beat yourself up over trivial stuff. A good chess memory allows you to laugh and forget silly mistakes.
I’m over it 
“I’m over it.” Yeah, sure you are! 
No chess players ever get over a game, they rehash it until they convince themselves that they should have won. 
If it’s any comfort, I looked at that position for 2-3 minutes before I figured out why you didn’t need your king to mate.
Bill Smythe
LOL I have been doing Tactics Burn-in yet again in my life, this time after being away from chess for over a quarter of a century, but this time I am doing it very thoroughly as I have the time. After doing a lot of it with a1 in the lower left no matter which side was to move, I have been looking at Tactics Times positions for a bit. That book set gives you the over the board view, which took some getting used to. When I saw this position, I went into brain freeze, knowing something needed clarification. Then I finally realized, we were not told where a1 was. So the brain freeze was a reasonable reaction for a change.