I don't suppose any of us have led exemplary lives whether before or since our diagnosis - I certainly haven't.
It is true that if you become much more than just 'overweight' and become obese or worse and morbidly obese, then you do increase your chances of becoming T2. However - it isn't automatic for every single person that's overweight and doesn't exercise - unless the person has 'other' stuff going on, in their insides. And if it was just 'lifestyle factors' - every single one would be T2, wouldn't they?
What 'other things' ? Well - how about every female in your family before you either having T2 already or all having Gestational diabetes when they were preg? or PCOS? What if there's a faulty gene or two in the mix? What if - anything ......
Nobody flipping well knows is the truth.
And I was 22 when diagnosed, and nobody knew anyone else in the family who had ever had any sort of diabetes, no extra big babies or anything at all that might give the slightest hint of why I should get T1 or my elder sister, or my cousin, both becoming T2 in much later life. However it's a big fat question mark hanging over both my sister's kids and my cousin's kids (all in their 40s by now LOL) - will any of them get it, or will it skip a generation or two or three?