Advice needed

Firstly, have you been confirmed by a Doctor that you have diabetes. I ask this as you have obviously experienced many of the symptoms of diabetes and were initially placed on Insulin, though you don't mention the Insulin after this only that you have been taking Metforming, the dosage which has been reduced of recent.
Many medical condition give the same symptoms of diabetes, especially where the kidneys are evolved. The prime purpose of the kidneys is to filter the individuals blood and remove the otherwise build up of harmful toxin levels in the bloodstream, by their filtering out these harmful toxins along with excess water into the urine.
Glucose in the bloodstream when it exceeds a threshold level is also filtered by the kidneys into urine, though the level at which this occurs is known to vary somewhat from one individual to another. In many cases the excess level of Glucose in the bloodstream will result in the individual passing a high level of urine as the excess glucose is filtered. Hence the thirst frequently experience and dehydration of having uncontrolled diabetes blood glucose levels.
Also the kidneys are prone to damage as a result of high glucose levels, ans a simple test on the urine of the individual can show if the kidneys are damaged as a result.
I hope that these answers will help you, should you need further help then please ask.

A Blood Glucose level of 41.6 mmol/L is certainly someting to be concerned about. No wonder you were instantly place on Insulin to bring this dangerously high level down.
I'm pleased for you that your B/G is now relatively 'normal' and that you are now feeling much better.
With sutch an initial level, it would most likely suggested diabetes of Type 1, but the reversal of these high levels without resorting to Insulin make me wonder if something else isn't the root cause. Ultimately the standard HbA1c blood test will show what your 'Average' blood glucose level has been over the preceeding 120 days and this will then hopefully give an answer to the mystery of your initial high B/G level.
I've never know of a kidney problem that has resulted in such high levels and wonder if there is anyone out there who can shed any further light on this.
If you are diabetic, then it's wise practice to avoid sugar where this is possible. The occasional breaking of the rules is something that I have been known to do, but with Tea the answer is simple - Try using a sweetner, it has the same overall effect without introducing pure refined carbohydrate directly rapidly into your bloodstream and boosing your blood/glucose level.