I'm glad the rest of the story got uploaded here. I remember being really invested after reading the 2nd chapter. I didn't end up loving it, but I didn't hate it.
I probably would've liked it more if the student/teacher stuff was actually some sort of ploy to make the MC jealous and the part where she sees the teacher kissing her fiancé was just some sort of unexpected, comedic road bump in the plan. Maybe have a chapter from the other girls' POV and reveal them bickering about whether what they're doing will work or if it's even morally okay.
The fact that there apparently were real feelings between the other two and their "relationship" starts so suddenly makes the whole thing feel rushed. I get the story is about "losing someone you love, if you can't be open and truthful with them.", so I get why one of the characters is a teacher who lost a girlfriend due to peer pressure. But, the story seemed more focused on the two younger girls figuring out their feelings and the "scumbag teacher" aspect just seemed like adding too much for only 4 chapters and an epilogue.