My main suggestion is to offer support and understanding for your fiance. Diabetes can be a real challenge. Try not to nag or be overbearing, but also tell him that you love him and would like to be of help. Ask him how you could help. Could you go with him to his medical appointments or take a class on diabetes, or read an up-to-date reference on diabetes? Tell him you would like to learn how to help him when his blood sugar is low, etc.
Some people with diabetes are tired of “well-wishers” telling them what to do, being the “food police” with statements such as “Are you supposed to be eating that candy bar?” They may also be very hurt by previous medical and nursing professionals who may have approached them with a judgmental attitude or condescending attitude. He has had many years to get to the point he is at. A loving relationship can make all the difference for him.
LM