Pulley System Question

[Vioz]

I just changed my belt because i noticed my belt was starting to rip up, on one side of the belt there was a nice long piece missing so it looked as if it was hanging on for dear life, thank god i noticed it doing an oil change.

Anyways, not sure how many miles you are suppose to change your belt, i hit 66k miles with my yaris and this was the first time i had to change it?

if its suppose to be every 100K miles of some sort do you think the NST pulleys have something to do with it?


Also my NST water pump pulley has a nice groove in it from the belt, should i replace it with a new pulley, not sure what is the average life on the water pump pulley but it looks like theres not much that pulley can take?