Josy can even have dialog on this. If the MC in the throuple "seduces" Josy, she'll admit:
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Interestingly, if the if the MC isn't on her path but still has feelings for her, she can say this instead if the MC "comforts" her:
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It's pretty clear Josy has very strong feelings for the MC despite her feelings for Maya. I think, in vacuum, she would choose Maya over the MC if it came down to it, because as she says, she doesn't want to be a cheater. But as we saw back in Episode 2, when things aren't in a vacuum it's not certain how she would act. If Maya keeps taking her frustrations out on Josy, she probably would choose the MC over Maya.
As I see it, that means the key to keeping Maya & Josy together is to help them find healthier ways to express their fears and frustrations when they can't be together. The real question is how to combine that with being a direct part of their relationship.