The bottom line is that the size of your eyeglasses doesn't match the shape of your face, it is lager. Or it is also possible that the temple arms become loose after being worn for a long time, you can adjust them according to your face.
The glasses are sliding down because the size of your eyeglasses maybe a little large for your face, or the nose pads don’t match your nose, you should adjust your nose pads to make them fit the height of your nose bridge.