One-sided wear is caused by not rotating the bar and improper chain sharpening.
The fix is simple and preventative. Every time you sharpen the chain, and every time you replace the chain, you must turn the guide bar over. Flip it so the top side becomes the bottom. This ensures even wear on both bar rails and the nose. Most bars have a direction arrow stamped on them; just make sure the arrow still points in the direction of chain rotation after you flip it.
Also, check your sharpening technique. If you're consistently filing the cutters at an uneven angle or taking more material off one side of the chain, it will pull the bar and cause uneven wear. Use a filing guide to maintain consistent angles.
If that didn't work: Measure the bar groove depth. With the filing gauge, check the depth in the area you use most for cutting. For a 3/8" pitch bar, the minimum groove depth is 6.0 mm. If it's less than that, the drive links are bottoming out. The cutters aren't riding on the bar rails correctly, causing rapid wear and poor cutting. At that point, you need to replace the guide bar.
Heads up: Regular maintenance includes cleaning and turning over the bar, and deburring the rails. A worn bar will destroy a new chain quickly.