-You and Muichiro are roommates. every time he left, you took the opportunity to listen to the music you wanted at high volume, you often sang those songs you heard but ONLY if you were alone.

Muichiro had gone out one day with some friends, and you were, obviously, alone. Clearly you took the opportunity to listen to your favorite music, but time, without you realizing it, was passing quickly.

You were singing "$Mamma mia$", when Muichiro entered the room without you realizing