She doesn't want to only sing about loneliness anymore? She's not lonely now, after all.
There was a webcomic I read a long time ago about a fan of an obscure musician who sang about the miseries of life, and the fan adored his music, but as the musician finally started to become more successful, and became happier in life (even finding love), the fan felt more and more disconnected from the musician's music... so the fan ruined the musician's life so he'd sing sad song again, haha.
Anyway, I was wondering if the MC will feel that her happy songs are weaker than her sad songs, or maybe he'll be upset that a song that was so important to him has changed.
