This can generally be explained like this: let's say a scenario where we have no feelings for Josy and we choose to just hang out with her as a friend.
MC perceives Josy as a friend, despite the fact that they had a small affair with her and doesn't count on anything, hmm.. "unusual". And all the initiative here, the creation of this romantic and seductive atmosphere is on Josy, because she has one-sided feelings for him.
What’s unpleasant is being a hostage to the situation while on the route. If I were MC, knowing that my girlfriend could be somewhere in this house, I would simply interrupt the event, saying “Josy, I’m sorry, but this is not at all right what we are doing now, it would be better for me to leave.” Moreover, I wouldn't take my pants off. Alas, the choice here can only be made on Others by making the control shot "Josy, I'm over you". On routes he just says I'm with Sage/Jill/someone(Isabella). The friendship is not fake - MC really wants to be friends with them and we cannot influence this, this is the main storyline, which is static. There are his thoughts and feelings that cannot be changed by the player, “fixed points in time,” as one famous character would say.
As for Maya, hanging out with her is more immersive because it gives us a choice with her legs - here we have more control over the situation. Maya also uses subtle psychological play with whispers, in contrast to the more straightforward Josy, who uses male instincts more crudely. But knowing the identity of Maya and Josy, if MC lost control of himself, would Maya stop him? I think yes. She has better control over her feelings. Not sure about Josy. It seems to me that Maya perceives this as light flirting, tomfoolery, without pursuing secret goals in seduction.
This two girls is very different.
By default, MC trusts Maya more than Josy. We can see this on Isabella's route. When Maya asks him to tell her about his girlfriend, he admits that she is Isabella. He doesn't tell Josy about this, as far as I remember. I have the same feelings. It’s logical, especially since we spend most of the time hanging out with Josy...gossiping.