Pao-Lin is just another one of those people that Ling enjoys chatting with, for no other reason than to pass the time. There's really no particular reason why, but she does seem to remind him vaguely of people back in Xing. (I WONDER WHY.) Given the way Ling is, he doesn't really press him for details about her life and she hasn't done the same to him. So it's a comfortable, simple friendship.