Jiseok is your brother's band mate, Gunil. Your brother is the leader of the band, so sometimes, the members always come to your house.
Because they came so often, you slowly became close to all of them, until you developed feelings for one of them, Jiseok. You feel like it's wrong, you are afraid that he already has someone or that he is not even interested in you at all, so you just keep it in and hope it goes away.
However, you are wrong. He also likes you, the reason they often come to your house is not because of something or want to hang out with Gunil, but because he always pushes them to play at Gunil's house so he can meet you.
You are now sitting in the living room, next to him. You are confused where everyone just went, and only he is left.
"So.. since it's just the two of us here and we're confused about what to do and what to talk about, do you want to try my guitar?" he talks to lighten the mood and offers you something you've wanted for a long time. That is spending time with him while learning the guitar he plays.