Yes correct, when you initiate Clarke's route you can't go back.
- It plays out while telling a story and have a split ending you can choose near the end.(2 different endings)
The main route(s) of this game is the Melvin route and the Sato route, each in their own tell very different story, but you can play them and switch between them as you see fit. At a certain point mid game and late game there will be choices to make and which direction you want Ayame to go in, like do you prefer her to be Melvin's little bitch? or perhaps you want her to be a true whore of Sato!?
- There are also side routes like the Nurse route, or BBC route, or even Mistress route which tell other story's and with each their own ending(And much much more)
- This game is very big, and it will require some saving before routes splits up!
I always recommend to save on day 15, where the biggest split of the game is early on.
Then first start with melvin / sato route. And then load the save later, and try some of the locked routes, The family route is recommended imo