A type 2 doesn't "become" type 1, just b/c they take insulin. Type 1s have an autoimmune disease, where the body confuses healthy cells fore enemy cells and starts killing these cells which produce insulin. Usually, Type 1s enter a state of DKA when first diagnosed, whereas Type 2s usually don't experience that. Type 2s usually make insulin, but in time could come to need to inject it to manage the disease.
It's confusing, but I hope I cleared it up a little
