Diabetes affects many parts of your body (I would know)
What happened is that your pancreas doesn't work properly. so the sugar goes to your red cells instead of its normal route.
The body parts that diabetes affects are
Eyes: diabetes can damage the blood vessels in your eyes especially if you don't take care of yourself.
Nervous System: to much glucose in the blood can damage the nerves in your body it can lead to numbness pain and you can loose your limbs to infection.
Heart: if you have diabetes, you are more likely to have heart disease or a stroke because your blood vessels get damaged and become narrow
Kidneys: high blood glucose make your kidney have to work harder and it they work too hard, it could lead to chronic kidney disease.
I know these because I have type one diabetes and it is NOT fun.