This is why I enjoy the most games that have a story that's completely independent from the sharing/NTR dynamics. A story that's focused on consensual sharing, and doesn't have any other main theme, has to live on the build-up, the slow burn discovery, and end after the characters have "sampled" everything that realistically can be experimented in that regard. That's where NTR can have a role, as an optional conclusion - at the end of the path, the way the reader's choices shaped their experiences, their reactions, etc can lead to a few different endings, one or more of them containing the elements you described, like gf stolen. Some people value the coherence in how these endings are determined, I admit I value most of all the ability to avoid any endings that destroy or degrade the monogamic relationship within the couple (including not only NTR but also the intrusion of other people at a level that changes the couple's dynamic drastically, such as throuple endings, cuckold/bull endings, free pass where the two aren't even expected to be each other's main partner anymore), while at the same enjoying all or most of the game's scenes.
Just to mention that in a game where the story is NOT centred around partner sharing, I find it's much easier to keep a steady flow of different scenes and situations without seeming repetitive or a citation of something some other game already pulled, providing the user with simple choices to skip unwanted scenes, without losing the flow of the main story. If this were category B and the previous category described category A stories, with respect to sharing, I'd say this game initially felt like a Cat. A (slow burn focused on sharing, with a hinted sense of progression (albeit some people complained that the hobo scene was going too fast, or even the policeman scene, I still felt like it was easing into the theme slow enough to warrant a few more episodes of it). But then it turned into a cat. B, with the development of the supernatural aspect that was merely hinted at initially. I'd hope it continues this path, as it's still the least explored, but has led to good good games, some completed, some ongoing. But I also hope the author manages to keep all the jealousy, dread and negative emotions neatly on its own path, possibly leading to an NTR ending if it pleases them, and part of the audience, but preserve a path where you, the player, can make choices that feel assertive and lead to reward for the MC, free of any masochism.
