This desire for cleanliness also makes Xiu more exotic to Lao Jin and so it can only strengthen his feelings for her. Though Xiu returns Lao Jin's love, it is a platonic, daughterly love that she feels, not a romantic or sexual love. It is possible that after all she has been through she may not be able to allow herself to feel any kind of romantic or sexual love, but even if she could feel this kind of emotion for Lao Jin, it would be in vain since the relationship could never be consummated. Lao Jin cares for her in the only way he can, which is by providing and caring for her needs. He is also a mentor and a teacher to her -- all of these things are part of the kind of relationship that one would have with a father...

Xiu may also have purposely avoided developing feelings for Lao Jin in a romantic sense because she fully expected to return home to her family at some point. It would have been very difficult for her to leave someone she cared for so deeply if her efforts to make it back home were successful. It's also for this same reason that she was seeking a father figure since her own family was taken away from her so quickly, and Xiu was so young. In this way Lao Jin came to replace her own father.
No matter which way you examine the love that Xiu and Lao Jin had for one another, this film is heart-wrenching and sad. The situations and characters presented are so frustrating to watch. The audience learns to feel sorry for both of these characters since Lao Jin will never be able to fulfill his love for Xiu in a positive way, and Xiu will never get home. It is this realization that bring the film to its inevitable end, which is the ultimate expression of the love these two have for each other.