Realizing that you're not here (原來這裡沒有你) - Eason Chan

Like this line of the lyrics

舊日尚未盡力共挽手到未來,今天終於分開未說出應不應該

In the past, I did not try my best to build the future with you; today, we are finally breaking up and I dare not say if it is a good ending for us