The lyrics of "I once loved you wholeheartedly" mean that I once really loved you wholeheartedly, liked you very much and wanted to be with you very much. The other person once loved you. She set herself a time limit for this love. Unfortunately, the other party felt that they didn't get what they expected, so now they gave up in despair.
I once loved you with all my heart, which was published in Pan Meichen on July 3rd, 2008. It is included in her solo album "Don't Go, Don't Go". The lyrics are like this: you are always so cold, but I am so lonely.