I'm on my 3rd belt in 525K miles. That includes the original. I also recently replaced my original tensioner and I'm now on my 3rd water pump.
Let me share my squeaky tale. I had something squeaking that I could not pin down. I pulled the W/P. It had a tight spot and a squeak when spinning it and it had over 200K on it so it got replaced. Pulled my alternator and took it to a friend that builds them. It had bad bearings and the stator was bad so it got replaced. I then replaced the tensioner, as I said, it was the original. The squeak was still there. I finally replaced the belt, the old one didn't look bad, with a new Gates HD and no more squeak.