Noise from crankshaft spindle and then the pedal falls off
Like I said, by now the crank arm is toast.  Originally the problem was just that the crank bolt was loose (they need to be REALLY tight -- ideally set with a torque wrench). 

But running with a loose crank has deformed the socket on the end of the crank to where it no longer fits, and it rocks and works the bolt loose as you pedal.  And by now the crank shaft (which is steel vs the aluminum crank arm) may also be deformed.

There is a vague possibility that a clever person could make the existing crank arm work fairly well with a shim cut from a beer can, but it takes some mechanical aptitude.