Why did the ninja turtles separate and who's the one wanted out?

Answer 1

I have not seen the film version yet but in the comics, the reason for the seperation is chalked up to the simple act of growing up. Take away the "Mutant Ninja Turtles" part and you are left with TEENAGERS. Young men who want to find themselves. Who want to be identified as their own persons, not as a collective whole. They all have different intests and passions and to expect them to always want to stay together is just as bad as expecting a set of identical twins have the same personality.