Why Does Serpentine Belt Break After Replacing?

Yes, your tensioner is stuck therefore its creating friction. And that's why the belt snapped

It would be my guess that the tensioner pulley would need to be replaced. If it isn't turning, then it is because the bearing is froze up.

Your tensioner pully needs replacing or you can spray WD - 40 on it to see if that works before changing the pully .

You could of had the belt to tight, or one of your pullers is froze up and will not move. Check your pullers.

My power steering pump broke, I replaced it and then my belt broke...I replaced and then it broke again...when I start it it sounds really loud.. When I was driving, I lost all power steering and the belt started squealing..any ideas?

You probably had a pyrotechnic pretensioner which when deployed, in a crash in excess of 12 mph, would have ignited.
The whole assembly should be replaced, following a crash.
The new assembly should be fitted and tested by a qualified technician. If this has not been done you may invalidate your car insurance and any parts warranty. This is not a DIY job.
You could also try contacting TRW Automotive/Seat Belt & Air bags division for more detailed advise. TRW are a USA multi national seat belt supplier to almost every car manufacturer in the world.
Good luck
Moonraker

You need to see if the idler pully is not locked up an it will turn freely if not replace it