2006 Ford Five Hundred

You were probably burning through serpentine belts because one or more pulleys were locked up, a simple check would have revealed that at the time of replacing the first belt. Assuming it was the AC pulley, which appears to have been the culprit, finally burned out it's clutch so it can once again spin freely, you should remove the belt and confirm it's indeed spinning freely. The 500 is a good car, but like any vehicle it needs maintenance.