Lewdlab understands internal conflict in these taboo relationships, which was one of Dreams of Desire's strongest points. It's been done well again here, as Joyce, Isabel and Ruby all have conflicted emotions regarding the MC that they need to navigate and transcend. I feel like with Joyce, it's easier, which makes sense why her relationship with the MC has been developed first. She's in a loveless relationship, feels as though time is passing her by, and wants to explore a side that she's repressed for too long. Essentially, she likely thinks that the moment is now. I'd also say that it's easier with Joyce because, like many women in her role, she thinks that the MC can do no wrong, sees him through tinted lenses, and loves him unconditionally.
Where it could get more challenging, in terms of the continuation of this relationship development, is with Isabel and Ruby. Realistically, I'd imagine that the MC would need to evolve more to earn their affection. Being younger and with more experiences ahead of them, it's possible that they believe they have more to lose if they decide to establish relationships with the MC. Isabel, as the main example, I can see moving on to pursue her ambitions and love life, which perhaps don't include the MC. I'm yet to see anything that stands out in the guy that she couldn't find in any other men her age, for instance. I think that a lot is riding on this older sibling affection on her side, plus maybe curiosity, to develop this potential relationship, which I don't think would be enough to seem realistic, from a psychology and literary perspective.
This is why I think something would need to be added in terms of writing ideas to develop the MC-Isabel story and, perhaps to a lesser degree, the MC-Ruby one as well. He just appears to be a young person who's too naive and not suited for the dark business world he's entered. In his position, I'd imagine that one would need to earn these points doing some pretty selfless tasks, for no reason other than wanting to do them; anything from giving them ideas which lead to success in their passions, helping them initiate business projects, or anything as little as making them hearty food when sick or on a bad day. In other words, the MC would need to demonstrate value in unique ways to leave some form of psychological imprint that goes beyond the sexual realm.
That's more or less where I'm at with the game, so far. For what it's worth, I'm into it a lot, and I hope it continues to get better.