So he probably blamed her for his failure. Prob she was insisting him to go back to university but he didn’t want to, gaming addiction causes temper problems so in the heat of the moment he said something he shouldn’t have said. Causing a big scar on her This making her into loner. She probably taught she was a bad influence to people she held dear hence she stopped socializing, but it had a reverse affect she didn’t realize it making the situation worse . The plot is easy to guess so far ( the source on the gaming addiction causing anger issues is me, I did go trough the same phase )