Chess Players?

[Xiahou]

The only other move is Kf1 right?

Yup. Which would've avoided the Ng4 threat, but would have deprived me of opportunity to play the 'oh so tempting' Re1 pin.

Black moves the knight forward and then… then what did White do?

With 11... Ng4, Black is threatening a mate in one by playing Nxf2 next turn. My idea was to pin the black Queen using my Rook. Ng4 would put that idea out the window, and instead I would've had to try to deal with a pretty strong mating threat. Luckily he didn't see it, and I won.