3 chapters is rough to finish a story with this many characters.
While the childhood friend is by far the least compelling, that's by design because we haven't seen much of her. We know she is lying about having a boyfriend and rejected his confession in the past. Narratively it's most likely either her or a cop-out open-ended resolution.
Overall most characters have barely gotten any time outside of their own personal arcs, which were fairly one-dimensional. The biggest exception is Meguru who set up the inciting incident and helped him investigate 2 of the 6 other girls. She's the only person that might narratively contest the childhood friend, but the odds aren't high.