Hi Mistee, Shop!
Type 2s do not become Type 1s by going onto insulin - it is a different condition (although Type 1s can get Type 2 in addition to their Type 1 - known as double diabetes).
Type 1 is an autoimmune condition whereby your antibodies attack your insulin-makin beta cells. Eventually they kill them all off and you cannot produce insulin. In children and young adults this tends to happen very quickly (a matter of a few days), but in some adults, it happens progressively over a period of months or years - this is known as LADA, Type 1.5 or late onset Type 1.
Type 2 is a metabolic condition whereby your body can produce insulin, but for some reason you are resistant to it and cannot use it properly. Your body then produces increasing amounts of insulin to try to bring your BGs under control. High BG kills your pancreatic beta cells and you are able to produce less and less insulin - at that point, you need to start injecting insulin. The problem is that your body is still resistant to injected insulin and so Type 2s frequently have to use large amounts of injected insulin unless they can improve their insulin resistance. Type 2s also often have other metabolic conditions such as high BP and high cholestorol.
Not sure if that answers your questions? If not, let me know and I'll try to explain more clearly.
Smidge