I'm type 1 diabetic so I can understand your struggles, and I'm sorry you feel this way. To answer your question, diabetes isn't my main reason for ctb but it's definitely a contributing factor. Though, I was suicidal a long time before my diagnosis. Not to discourage you in the slightest, but my control isn't even that bad (worst hbA1c was 8.4, last one was 7.2 %) and I've already shown signs of complications, namely neuropathic pain in my legs mostly at night. It gets worse when I lose control over my blood sugar, lately I haven't experienced much pain since my control is better. Similar to you, I've been diagnosed 3 years ago. The reason why diabetes is so distressing to me is that even with tight control (which is near impossible to achieve...), you can develop complications. I'm a nursing student and nothing brings my mood down like seeing all the diseases associated with diabetes: cardiovascular and kidney disease, chronic pain (neuropathy), infections, slow to heal wounds, high blood pressure, stroke... the list goes on.
Though I'll have to highlight something that's bugging me : are you sure it's diabetes?
I'll be honest, I've never heard that sun exposure, or vitamin D excess, plays a role in developing T2 diabetes. As others have mentioned, diabetes is very complex, and could be caused by so many factors unknown to you (insulin resistance, inappropriate glucose storage by liver, etc). Hell, my grandma has been active and ate well all her life, but has been diagnosed T2D. Actually, sunbathing always causes me to have low blood sugar, because insulin is absorbed more quickly in high temperatures.
My second concern is that what you're suffering from isn't actually diabetes, since you haven't been diagnosed.
Some other illnesses share the same symptoms as diabetes: thirst, frequent urination, increased hunger yet gradual weight loss, frequent infections, blurriness in vision, chronic fatigue...
Some of these look a lot like thyroid imbalances, for example, so I'd be worth getting it checked out.
With all that being said, I don't wish to take away from your experience. I know how much diabetes reduces your quality of life, not to mention how it's not even taken seriously sometimes. I do wish to add that you're not a hopeless case. There's still time for you to get diagnosed, and stop the progression of eventual complications. It's a disease that never truly stops progressing, but just getting meds could significantly improve your quality of life, especially since diabetes is a factor for ctb. For example, depression is highly common in diabetics. I do understand that it's not your only reason for wanting to ctb, so I'd understand if you're not willing to undertake treatment. Please ignore my advice if it doesn't seem helpful.
In the meantime, stay hydrated and limit your intake of foods that can spike blood sugar (ex. trade white bread for brown), to avoid symptoms of hyperglycemia. Just avoiding high blood sugar can make you feel much better in my experience. Wish you the best.