What's so hard?
There was no mate threat from 11 Nd7??. (The knight on e8 defended g7.) You could have taken the knight with either the bishop or the queen.
Black's best response to 11: Nd7???
Sort:
Mutual blindness to the 9th degree. It happens. Better here than in an OTB tournament. Delete your post to discourage the trolls if you can 
I'd suggest some time focused on tactics. Since you are not a paid member here, check out chesstempo.com which offers better free tactics training.
My opponent took over 3 minutes to make this move, and I couldn't blame him. I still cannot determine the best possible response.
For the record my opponent says he meant to play 21:...Bf6 instead of f6. He threw the game and resigned after.