Like
Bibifoc said, you can only get the scenes with Amber if you send Dylan to boarding school, so have left the main Dylan route. Nothing to do at all with playing the Sam route or not.
I do find it curious listening to many complaining about how the routes are so disconnected, when I've had the completely opposite experience. During the Yoga event, Sophia muses about how relaxed she is about getting naked now, having shown her boobs to several women that day. And Ellie commenting on how nice and quiet it is without Dylan around.
But then I also don't play the routes people are complaining about, so I don't know. I'll have to see if I feel the same way after the next Ellie event.