@nep A plot summary might be similar at that level, but the works you cited are from different authors/sources.
The work you refer to is School Days. I only ever watched the anime but the original work is a visual novel. Those works were produced by people who are
*not* Hiroyuki, the author of this manga and Aho Girl.
If I'm wrong then I'm wrong, but I highly doubt that an author will write a story they don't want to write. I don't think Hiroyuki is interested in telling stories about two-timing that result in a trail of blood and dead bodies. I think the polyamorous ("two-timing") relationship here, which has so far been depicted with extreme honesty and respect for all parties in the relationship, is completely different than the relationship in School Days, where the MC started dating the first girl, and then started sleeping with the second girl behind the first girl's back, then started sleeping with every other girl in class, then started ignoring the first girl, then etc etc etc spiral into a sad vortex of bad decisions and angry retaliation. This work is nothing like that.