Å·±¦ÓéÀÖ

I think it was because she was struggling. She was unhappy and as explained in the books she had got herself in to a number of scrapes with the whole ghost thing. She was a young girl struggling with who and what she was, despite her 'kick ass' attitude. He left when Jesse became a living person again and Suze had discovered who and what she was. In its simplest terms, he wanted her to be happy and at the end of the book she was.
This is just what I thought...

Well, it is said that ghosts do not leave earth till they fulfill their goals. His goal was helping his daughter make the right decisions, so maybe that's why he stayed...