I forgot to describe one part:
The Cheating route in this game just look the same as the cuckold or sharing route, because in the 3 routes she is giving herself.
I think cheating route should be me a thing the character be ashamed of doing, avoiding and being reluctant, not giving herself. Because if she does on her will at least for the start of the relation with the outside partner it just looking the she loves the other. And also the her partner don't need to be a asshole to her or do not provide "enough satisfaction".
That is why I say male MC don't need to be a dick and also can satisfy her needs (as in affection and sex), so she doesn't want to cheat, but she got enough coercion from others (not forced cheating) and she being a lot reluctant at the start, and being less the development with others progress.
For me the 3 routes looks the same, and I though cheating would be more reluctant.