Crank arm replacement for an idiot

[acbenson]

Hi,

I would if anyone could help?
sometime ago, I clipped a kerb with my nearside (to kerb) pedal, resulting in this crank arm falling off.

Since then I have been unable to get the arm to stay on the bike, as I pedal the nut holding the arm in place loosens, the arm begins to wobble and the pedal/arm falls off :-(

I have 3 parts, in the pics attached, crank arm, nut and the hub. what I am missing?

Thanks
Tony
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