Madison - First of all, Happy Birthday! It seems like the last thing you need is a happy-go-lucky response that doesn't resonate with the turmoil you feel. You've been given many wise responses here. If you haven't, read them over a few times. Sometimes it takes a while for ideas to sink in.
All the feelings that you're experiencing are legitimate. But they are not the final judgment about how your life will unfold. I had all those feelings you write about but at a a different stage in my life. I was 30.
I now benefit from a much longer view of things. I didn't like when my parents pointed out how their perspective moderated how they viewed the same event as me. Part of my anger derived from the fact that in a part of my heart, I knew they were right.
Some people with diabetes would argue that there is nothing good about diabetes. I take the other side of that argument. Diabetes has amplified many good personal traits that were not so well expressed before my diagnosis. I am now much more attentive to my health needs. I learned to put these needs first. Some might say it's selfish but sometimes you need to love yourself first before others can love you. In fact, how you treat yourself teaches others how you want to be treated.
Diabetes has helped me become a much better me. Life carves and erodes every physical thing in this world, man and nature. No one gets by unscathed. Its the nature of living. Please know that the sadness and grief you feel will later help define define your capacity to feel immense joy and fulfillment, if you let it.
Be kind to yourself and give yourself the time you need. Things will not get better overnight, but sometime in the future you may find yourself busy with some important project and it'll dawn on you that you feel happy! Life can surprise that way.
Whenever I've gone through crises in my life I always fell back on the fundamentals: get plenty of sleep, eat nourishing food, exercise, drink enough water, and express your true feelings to at least one other person. It's never let me down even in the face of health loss, love gone wrong, and death of loved ones. Take care and notice one beautiful thing today, whether it be the fragrance of a flower, the rich color of nature, or perhaps a friend's smile.