Yes, it was intentional. I didn't want those who did not want to explore that kind of relationship to feel like they had missed something. I will be including it in the gallery eventually though - it will be the last CG of Sofia's route (in the gallery) and followed by the CGs from Frederique's route.
I felt this was the best way to handle it, as anyone who does not want to explore that kind of relationship will be missing all of Frederique's CGs (so the missing Sofia CG will be less noticeable), but the CG will still be there for those who want to see it again.
I hope that makes sense and thank you for your interest ^_^