He is saying he always wanted out of the crime business and wanted to be legitimate. Let's not be fooled my Michael... he clearly didn't want out of the business at all, even by the end of Part III until Mary was killed.
I think many see this incorrectly. He didnt really want out? Why because he didnt go legitimate all at once. It would have been suicide for him to take his fingers off of some of the strings. Going legitimate for the Corleone's REALISTICALLY would have taken atleast one full generation after Michael. Thats why he wanted Tony (he throws away greatness).
Slowly, one by one you cut the strings from the puppet masters hands. Not all at once. You are then exposed and vulnerable.
