The ending paths(happy or fallen) are like that, though not always the same choice for each girl.
The in-game indication is the contents of the message, however without a good translation it isn't much help IMO.
The path to acquire all the skills involves sending 15 replies (with the 16 triggering an ending).
This is convoluted, so I tried to simplify the path that works.
There are actually 4 things that can happen for each response:
1. Trigger the next happy path message
2. Trigger the next fallen path message.
3. Get locked out, will require investigating bag to get next message.
4. Messages stop.
To get the 16 messages it is needed to get messages from happy and fallen path, it gets tricky.