Hi~

Hi guys~
looking for a manga. In specific i'm looking for the squeal of the one i'm describing but I can't seem to find either one of them so :')
high school student x teacher.
teacher is into cute things, specifically into a jpop boy group. he got into the boy group because he went with his sister to a concert when he was younger, and fell in love with the group.
the day before he starts going to teach part time at a school, he goes into a music store to collect a package (a fan item of the boy group) . a student (that he does not teach) works there, and the teacher does not recognize the student, but seems to think that the student is familiar in some way. the next day the student and the teacher see each other on the train and the student makes a comment about how the teacher always orders or something. the student starts to tease the teacher about his obsessions and it is eventually found out that the student is the younger brother of the main singer (?) or leader/ actor of the boy group that the teacher is extremely fond of. it turns out that the brothers have a strained relationship, that gets somewhat fixed by the end of the manga.
the squeal has like one chapter i believe, and it is about the older brother and it reflects on his past prior to the events discussed above. it turns out he was in a relationship with another guy, during their trainee days, but had to break up due to company issues. the older brother is still in love with the guy (or so it implies).
Please help if you can!