His disappointment over the reason that he wasn't able to see her and talk to her before she left had made Feng Tianyi decide to forget what transpired during that short trip he had with his godfather. He was forced to accept that he wouldn't be able to see nor meet Yu'er again.
Just as she said during their first meeting, there's no need for them to know her name, as he would be forgetting about her soon anyway, or so they thought.
Why hadn't he asked her real name? If he knew who she was, perhaps it would be easy for him to find her in the future, but the question was still: why?
True. The few weeks he spent with the little girl was something he never had with anyone before. Because Yu'er was a few years younger than him, it was his responsibility to look after her whenever she was with him.