Shun's younger brother Fuyuki and his girlfriend Mamiya-san kissed.  When Shun finds out, he asks his friends what he should do as Fuyuki's older brother.
Fuyuki ignores his brother and goes on a date with Mamiya.  The gang decides to follow the couple on their date and end up at a karaoke box.
Shun asked me about it, 
so I had to tell him.
Shun me preguntó al respecto, así que tuve que decirle.
Shun me preguntó y tuve que decírselo.
O Shun perguntou a respeito, 
então tive que falar.