quietann

Listen to your mother. She isn't stupid, and she does understand. Plus, listening to her will improve her relationship with your father.
Pressure your parents harder about letting you go to college a year early.
Your brother may be an annoying kid, but he's going to turn into someone wonderful.
You are not nearly so ugly as the world around you has led you to believe.
The anti-depressants that will help you are still in the future.
Stay active. Keep riding (bicycles and horses). You aren't at a competitive level and your physical limitations mean you never will be, but that doesn't matter. You don't need to be at a competitive level in everything.
At the same time, get away from the scale. It is your enemy, a very seductive one that gives you "true" feedback at any hour of the day or night.
Of those two boys you like, pick the one who likes you back (the one who likes girls in general, though the other hasn't gone completely gay yet...)
Girls are beautiful. Don't ignore them in favor of boys.
The diabetes isn't going away. There are things you can do to make it better, to feel better. Do them.
WRT diabetes care, staying active, and so many other things: if you are not perfect at them, that doesn't mean you shouldn't keep trying them.

for my 16 year old self...