The crankshaft pulley on my 2001 Camry in no longer aligned with the other pulleys, so my alternator belt does not stay on
The crankshaft pulley or harmonic balancer has a rubber ring between the pulley and the hub that connects to the crankshaft. More than likely the pulley part of the balancer is slipping off this rubber ring causing the belt to become misaligned with the other pulley’s. If you look close you might see some of this rubber ring starting to be exposed.
The fix is to replace the harmonic balancer.
I had this problem last summer on my wife’s Oldsmobile. It was a loose harmonic balancer bolt. I replaced the bolt with a new one and it’s been fine ever since. If the bolt is tight then follow Tester’s advice and replace the harmonic balancer.