I am not sure you understand the kink and are letting hentai tropes seeping in. Submissive or not, it is still a consensual sexual play. Submissiveness is about surrendering control and the sense of degradation is still within the consensual and trusting dynamic of the relationship. It wouldn't work without the trust, because then it just becomes cheating and abusive.I agree with you on almost everything.
But I will add a new concept.
The girl will not leave her useless boyfriend but will shift her love and desire interest to a more attractive partner.
If we draw parallels with the game, then Nathan is the most suitable candidate - he shares her interests , physically and emotionally attractive to Laura, the girl's besties approve of him - as a result, she will spend more time with him and his interests and desires will become a higher priority for her than the interests of the ms.
As a result, over time, the ms is simply a fifth wheel or just falls into the category of ordinary Lauras bulls.
I think that the most probable ending of the submissive cuck route.
by the way, a great idea for an achievement - the fifth wheel )
Laura moving her love and focus to someone else, leaving her partner as a fifth wheel, has nothing to do with being consensual or trusting.