There's supposed to be extra scenes or something when you are on the Melody only path, well I've played through it twice and tried to stay on a Melody only path (ignoring all the other girls) and other than cutting out scenes with other girls I notice no difference.
The additional scenes are right at the end of the current content.
After you have sex with Melody, you have the option to repeat in 2 different positions (spoon & reverse cowgirl).
And you don't have to completely ignore the other girls.
Just make sure they are all "locked" by the time you blindfold her for dinner.
The exception seems to be Xiane.
The game seems to remember that you have started on her path if you get the massage in your apartment.