[s...starting with a slight recap this stuff is confusing :|a]
...On Sakura's seventh birthday, she was cursed with a death seal. I left my family and home to stay in Clow and find a way to remove that seal, but I failed, and on her fourteenth birthday the seal consumed her. I told you that I was offered a wish, to rewind time to that day in order to save her, and that I chose to make that wish.
The price for that wish was 'freedom' and 'time'. For the time that I rewound, until I once again reached the age at which I made that wish, I was with Fei Wong Reed. He planned to scatter Sakura's memories -- or you might call it her 'soul' -- across the worlds in order to force her to travel and retrieve them.