autobuss

It is Do Hyun who breaks up with Song I after becoming angry for the second time when she spends some time with Tae O. I cannot see a fault in Song I here, it is not her who breaks up. Do Hyeon shows as much jealousy as Tae O's GF and the two break-ups have the same motivation.

Have you watched the prequels? They obviously made the prequel episodes after the regular ones, so they had to deal with what already happened. Like trying to make up how Darth Vader becomes an evil guy, when he started as such a sweet, loving boy :-) . If you watched the second prequel, you kinda see how the teacher has it all planned "for the good of the students". Just... kinda.... not 100% believable.
Still, there are some details that are too much. They obviously couldn't change them... so they did their best, but couldn't work miracles. Possibly, the writers for the prequels were not the same as the original ones.
The only way to really serve justice to the show would have been to add some time-travel to fix things up. Maybe next time :-)