Poor Decisions

My first error was the decision to play chess on my phone while walking my dog. My sunglasses made it more difficult to see the phone's screen clearly in addition to other distractions. My opponent, rated 600 lower, held his own until I blundered from this position. In fact, there were several blunders as the advantage switched back and forth. 

White to move

58.Nc6??

58.Nb5 is how White stops the e-pawn. To my relief, this blunder was the game's second to the last.

58...e2?? Nd4+ and White has an unstoppable pawn.

What was the move Black should have played?

Knowledge of the square of the pawn and of the floating square is useful.