I too find Maya to be a very believable character and a sympathetic one at that. I've always felt like she's a victim of circumstance and so too her feelings for Josy were based on her circumstances.
It would seem that Maya has come from a very religious household with a somewhat controlling and very devout Dad, and that she never really had much chance to express herself. So there was probably some emotional and psychological repression going on with her, and people like that will often latch on to anyone who gives them some kind of positive affirmation which they don't get at home.
She mentions that she had gone on dates with a couple of guys but that she'd only ever been with a girl, that girl being Josy, so perhaps things simply didn't click with these guys on an emotional level but they did with Josy because perhaps she gave her this positive affirmation she was craving and thus Maya developed romantic feelings for her. Maya would then have taken this to mean that she is gay, but a connection like this with Josy would have been one born out of circumstance and not necessarily indicative of Maya's sexual orientation as there simply hadn't been any guys who elicited those same sorts of feelings.
Enter the MC. He is there for her when she most needs it, having seemingly lost her two most significant relationships with her parents and Josy, and he gives her affection, vaildation, and comfort somewhat unconditionally, as well not judging her too harshly. So this essentially unlocks hetero feelings that Maya didn't think she had and it confuses her because she thought she was gay when it may just have been a case of having a lack of options that formed her feelings for Josy.
So, in my view, Maya was never actually gay, she only assumed she was because she formed an emotional connection with Josy that developed into romance. But had the MC, or a guy like him, been there for Maya at the time Josy was, then she would be in a relationship with them and consider herself straight.
