哼着那首曾经的半情曲唱着那首曾经的半情歌
[hēng zhe nèi shŏu céng jīng de bàn qíng qŭ chàng zhe nèi shŏu céng jīng de bàn qíng gē]
Humming tunes or singing songs about half-felt love implies reminiscing about an unfinished or unfulfilled romance, filled with mixed feelings, nostalgia, or even melancholy.