This comment contains information regarding Murmur and unlocking the full gallery.
So after hours of playing Murmur and researching online for information, despite how bloody vague all sources I chanced upon were, on how to unlock the full gallery I have come to the conclusion that there are 2 paths to this game.
Pure Love or Corruption.
Corruption is most likely the path that most if not all players will start with due to a lack of knowledge of the game. To fully experience all the juicy bits of the Corruption path the player must ensure that they corrupt the girls as often as possible. They can mix in scenes belonging to the Corruption or Pure Love path as well, they just have to be smart about their choices.
The Pure Love path is the hardest to stumble upon unless you're a saint or vanilla enjoyer. In essence the player must NEVER choose a corruption dialogue hence why I call it the Pure Love path. I don't know if that will change as the game receives more updates or not, but I have completed all that was available in the game without hitting a roadblock in the Pure Love path. So if you're having trouble unlocking some gallery scenes try the Pure Love path.
Thanks for the game DD.