Man it's the we love each other but we miss the hints and think it's one-sided. It's a bit frustrating but it's not that bad.
Anyway, it started when they're in school. Uke was in a band and seme was in a baseball team. On the day seme lost his last match, he kissed uke and they grew apart since. They re-encountered again in the future in a adult hobby orchestral band.
Dolce na Bokura no Koi ni Tsuite