Yes, it's one of the false notes in the story. Especially glaring if the MC later enters the M/J relationship at the end of episode 4.
I know they have that ridiculous picnic scene where Maya basically gives MC permission to fuck around but, it just seems weird that they wouldn't be concerned that the MC is already in some kind of relationship with Sage. And Josy is also aware that MC is dating Jill as well. It all just heightens the impression that the MC isn't really a part of their relationship and is in fact a 'boy toy' for them to play with.
I wouldn't make it about Maya and Josy, it applies to all of them.
they pretend nothing happened
Bella knows about Jill, should have figured out about Maya and Josy (expecially if Mc went to her in the forth), and should have too some suspicions about Sage
Jill knows about Josy and therefore Maya, she may have suspicions about Bella.
Sage is the one who's a bit more on the sidelines, she can only know about Josy and Maya if Mc went to see her in the 4th.