Me too, for basically the same length of time. Honestly though? I suspect my depression comes from dealing with the symptoms and treating myself more then a direct symptom. I almost never complain but... shots suck! Glucose testing sucks! Dropping low and making an absolute fool of myself crying and shaking sucks ass! Having my muscles get eaten alive by acid because my last vial of insulin cooked in my pocket while walking home after my car broke down SUCKS! It's more then enough to make someone depressed.

I'm a type 1 diabetic and when I was a teenager and young adult I ended up developing such a high degree of resistance (my ratio was 1 unit for every 3g of carbs at the worst) that I nearly made myself into a type 2 diabetic as well. Genetics has some role to play in that but mostly it was me being a idiot. I got diagnosed at 22 months and by the time I turned 14 I had decided "F*** it" and just started doing whatever I wanted. However by the time I turned 21 after being hospitalized over a dozen times in like 7 years and my kidneys starting to fail. I finally got my s*** back together and started taking care of my self. Now a decade later I've somehow managed to come back from the edge, no protein in my urine and my insulin tolerance is in the average range for a type 1 my age. I bring it up cause I feel it is anecdotal evidence of the effects of varying resistance. A type 2 that let themselves get to that point would have never gotten themselves back to normal resistance levels again.

I always heard it referred to as delayed onset type 1 by endocrinologists. It is possible it was referred to as 1.5 at some point though. Most of my terminology comes out of late 90s early 00s when I was participating in medical studies for diabetes. I'm obviously still diabetic but I just see a GP now since specialists are expensive and hard to get in to see. So I don't have as much up-to-date terminology and things have changed a lot in the last decade.

Like the other poster said there is a know link between type 1 and depression. This is talking about insulin resistance though. Which while type 1s can develop insulin resistance it is a key facet of type 2 diabetes. Type ones with insulin resistance used to be called type 1.5 because it effectively having type 1 while also having type 2.