It's so interesting that people can view the same thing in such different ways because I personally don't feel that Maya did mistreat the MC.
The way I see it, when Maya first met the MC and told him that she had a boyfriend, that was a reflexive defensive measure she's likely used for many years to keep guys away from her, something that she pretty much admits to the MC when she begins to feel comfortable with him. Maya has obvious trust issues and I've seen some criticism of her asking for 100% honesty from him but not giving much in return, but the reason she does this is likely because she needs to know that someone is trustworthy before divulging the truth of herself. She's worried that if she tells him everything about herself before he has given her enough reason to trust him that it could ruin a potentially positive friendship. This is most likely tied to her Daddy issues as it's abundantly clear that he's not happy with her sexual orientation, and she may have also been bullied or seen others be bullied for it at school which would also contribute to a reticence to trust someone with the truth, especially a guy.
As for Josy, she was Maya's close friend who blossomed into her first love, the first person with whom she could be her real self. That's difficult to let go of, and this leads to Maya being understandably conflicted when doing things with the MC because not only is she confused about these new feelings she's experiencing for a guy but she's also unsure of where she and Josy stand at this point as well as feeling a little guilty for cheating. But her feelings for the MC are, I believe, genuine which also contributes to her inner conflict and she certainly wanted to tell the MC about her girlfriend and about the troubles they were going through, but she was probably thinking to herself, "do I even have a girlfriend anymore?". She probably thought she would never see Josy again and that the relationship was done, so didn't feel the need to ruin the good thing she had going with the MC by telling him about someone who she likely thought was no longer her girlfriend.
Overall, I see Maya as someone who was just trying to shield herself from being hurt and as such she was very guarded, something she admits to at the end of Ep 4. She also appears very remorseful for doing this with the MC and says that she should have let her guard down more him which tells me that, even though they've only know each other for a short time, her feelings for him already run pretty deep. She didn't mistreat the MC in any way, she just had trouble letting him in for a number of reasons and she herself recognised that, which is why I think her actions are forgivable, and even if you choose the friendship path with them, I can certainly see Maya coming back to the MC because of these feelings.
