Kareshi Kanojo no Jijou Chapter 80 Discussion

Ok so he changed two years ago? What happened 2 years ago I wonder?

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                        So, I guess it is certain then that the two of them will meet pretty soon. Although I can't help but wonder, what changed him 2 years ago? Very curious to know what it was that made him stop cursing the world (I think that is what they were implying since "he sounded like he was cursing the world in his playing" followed by bu 2 years ago his sound changed.)