You guys think this is a common misunderstanding trope, but you have to understand Haru is completely justified in this case
Legosi is a tard when it comes to love and have no idea what proper communication and talking out is beside thinking about his action
He never learns from his fucking up (love wise) and dont treat her girlfriend with appropriate level of attention, while he just goes off to save the world in some masochistic manner
He even left school without talking to anybody, not even her own girlfriend, while hanging out with some random sheep milf in the shittiest part of town
That is a ground for break up if you ask me. Im even more surprised that she didnt break up earlier