I opened the chapter and saw it wasn't best girl... so I left. Let me know when she arrives.
Never. She died. So you are finally free from having to follow this series.
**To respond to your edit: He literally has no girlfriend or romantic partner in this series. The
entire point is he's an oblivious moron who, despite knowing this world is not like his own, proceeds to act friendly to the point of near-intimacy with every woman he comes across with no regard for "interpersonal distance etiquette", and gives five different primary heroines "The Wrong Idea"--including the very ones you name.
At this point I'm just confused as to why anyone is surprised by this turn of events, even without reading the source material. This was telegraphed from the outset, when it was revealed that one of the Five Main Heroines of the Gender-Reversed World Harem Manga was in middle school.
Get upset, that's your prerogative, but acting like this came out of nowhere tells me a lot of people in this thread haven't actually been paying attention to what they're reading.
Especially as this whole series has been telegraphed to be horror in disguise, and things are absolutely gonna be trending south
real quick from this point onward now that Masato is suddenly made aware of the fact that he's fucked up, and has been fucking up from Day Dot.