Alekhine's gun dropped in quicksand

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PuzzlingManeuvers

I think the title sums up what happened. What I would like is some explanation on the thinking process to either play Nb4 or Qb4 after Qd6 instead of what I did, by dropping Alekhine's gun in quicksand. I didn't mean to evil.png

 

Any other comments in the game are welcome too.