Why does a serpetine belt keep coming off. on 1998 Chevrolet Monte Carlo

The origanial belt was replaced a few years ago, then all of a sudden the belt came off. Replaced it with a new belt and it will not stay on. Could it be the auto tensioner is worn out?

Asked by for the 1998 Chevrolet Monte Carlo
My suspicion is the auto belt tensioner is worn causing the belt to misalign with the other pullies.