Please Help Me Find The Manga

I'm looking for a bl manga whose name I've forgotten. It's about a teacher who went to a concert with his sister and he fell in love with the boy group. He goes to his nearby store to buy cd's posters and such from the band and the new guy turns out is a student at the school where the teacher works at. Later as they end up liking each other the teacher finds out that his bf is the lead singer who he favorites is his brother