It is worth reviewing JAR-FCL3 as it outlines the conditions that are compatible with class I and II cert.
In terms of diabetes mellitus there are two main types affecting adult males.
Type 1 diabetes: results from the body's failure to produce insulin, and presently requires the person to inject insulin. (Also referred to as insulin-dependent diabetes mellitus, IDDM for short, and juvenile diabetes.)
Type 2 diabetes: results from insulin resistance, a condition in which cells fail to use insulin properly, sometimes combined with an absolute insulin deficiency. (Formerly referred to as non-insulin-dependent diabetes mellitus, NIDDM for short, and adult-onset diabetes.)
Type 1 makes you unfit to fly and you will not be issued with either a class I or II. However based on your history you suspect yourself at risk of type 2. It is possible to get a class I with this condition provided the condition is correctly managed and with regular specialist and AME check ups.
You have done the right thing correcting your previously unhealthy lifestyle.