The game is enjoyable, but it misses one significant thing to make it great - an actual sense of progress to the girlfriend's corruption.
And implementing one, even with all the already present content, wouldn't be too difficult.
Have each character she "interacts" with have a specific kink/fetish tagged onto them - BDSM, humiliation, bestiality, breeding, lolis, cum eating, bondage, hidden NTR etc.
Once the girlfriend starts engaging with a given character, her reaction to said fetish becomes more and more enthusiastic, until she gets tagged with it herself.
At which point, when having fun with other characters, she unlocks scenes featuring said kink/fetish with THEM in turn.
That way you gain both a sense of her becoming increasingly lewd and depraved, with a nice list of fetishes being added into her as a visual aid, and also a reason to go back to already "completed" characters to see the new scenes.