My driver side strut needs to be replaced, do I have to get the other side replaced as well?

I would do them in pairs ...........................

It's usually prudent to replace the struts on both sides.

It depends on YOU.  ARE YOU forgive the language A FAT MFer that really needs exercise because you weigh half a ton?   Then you prematurely wore out that side of the car.    If ye be light as a feather, then if one is wore out chances are the other is close to being history too. 17 years is a long life on a strut.  While you don't HAVE to do the other one now, that means plan on booking yourself in in the near future.  If the mechanic recommends it, follow his recommendations.  He suggests it only because he KNOWS how soon the other one will go. Meaning more time for you to waste waiting for your car to get done.  You value your time?  You get it done in one go. An 03 car can and will many times last 30 years or more.  Even a Pontiac.

Ya, best to go with pairs. I know you save a little on labor doing two at once versus one now and one later. They have to do a wheel alignment when they remove the struts, as well but most of the time the labor to do the struts includes an alignment adjustment.

I always assumed yes, but amazingly it was a main dealer that told me I didn’t. 

My car had a rear one replaced after 4 years and then the  same one again with the other rear after 14 years. 

The fronts are still original.

You don't "have to" but with a vehicle that old it's the best thing to do. See if you can get a discount if you do both sides at the same time.

You're an adult. While there are many things one has to do in order to survive, replacing both struts isn't absolutely necessary. 

Yes or unexpected handling may result.

It all depends on how long you plan to keep the car.  If it was my only mode of transportation and I thought the car would last 2-3 more years, I would do both.  After replacement, be sure to do a wheel alignment.  The total value of your car is about $500 but if its in ok shape, and if you need it to go anywhere and drives from point a to b, then I would get them replaced.  This is not the time to go for another car without a buy back program which could be coming if the virus last much longer.  So expect similar govt programs like the 2009 car buy back program to come, but the only issue is that it will need to be driven there and you don't know when that program will be announced. 

Lastly, you can not replace the car for the cost of doing this work.  If you could, then I would get something younger.  To be fair, My 2001 Grand am GT sedan, was loosing transmission after 240K miles in 2012, so I replaced the car.  Your car was probably well taken car of if you are thinking of repairing it.  Good luck.  

Most people replace both at the same time. If one is bad the other probably isn't far behind