A treatment is something that health care experts do to control a patient's health problem, lessen its symptoms, or clear it up. For example, insulin for type 1 diabetes is a treatment that helps people live normal lives. A cure is when a treatment makes a health problem go away and it's not expected to come back.
The best thing you can do is be yourself and enjoy a normal friendship. Since diabetes is a part of who your friend is, you'll probably find you both talk about it at times. You'll want to be there to offer support when your friend needs you, and there are some helpful things you can do to look out for your friend. But it's just as important to share other experiences together.