Hills are where weight becomes a major factor biking. This is where having the correct gearing and using it properly can make or break a ride, Especially if a person is overweight, Or has other issues.
I find using a low enough gear, Even with moderate effort most hills are no different then riding quickly on a flat, or against some wind. The goal is to maintain a cadence of about 60 rpm, Where ones speed might drop to 3 - 4 mph on steep hills. If necessary, Walk the bike on the steepest parts.
A bike with a triple chain ring might be enough for a low enough gear with the 28 chainring & 34 sprocket for even an unfit person to get up most hills, Just not very fast. A single chain ring with 7 - 9 gears may not go low enough with a 42 chainring & 32 sprocket.
I'd also consult with your doctor about the safest way to fitness with your diabetes. Also don't ride until you are completely exhausted. This is not only frustrating after a ride, But can rob you of the motivation to ride again. Walking might be a better activity for you for the time being, Or at least a combination of the two. Stairs and hills are good to walk, Even slowly.