It's about having done something to someone or yourself which involves someone else, that you regret and can't stop regretting. The memories of it still haunt you. But at the end of the song, it is said that the future is not set, and you can still have a chance in the future, but you must still cope with (that) regret (of the past).
It's about having done something to someone or yourself which involves someone else, that you regret and can't stop regretting. The memories of it still haunt you. But at the end of the song, it is said that the future is not set, and you can still have a chance in the future, but you must still cope with (that) regret (of the past).