Tailor Tales is made in such a way that you can only read one route at a time. Switching over to a different route means losing your fierce/kind tally points of your current route and making each chapter more expensive. You can still go back to Neil's route if you'd like, by selecting one of the chapters you left off on and click 'new route' when prompted. You'll start at 0 Fierce and 0 Kind points though.
Basically you're meant to play and finish one route at a time ;)
You can always re-read chapters you've unlocked though!