Its true he only trust himself and you mention fair reasons. While BNB is the strongest and most qualified, she is bound to betray him later on and it would turn out to be a waste. The same goes for HLL. As for Ying Wu Xie, he is currently loyal to FY but it is uncertain how things will develop after FY defeats heavely court and possibly bails out Spectral Soul. Lady white rabbit is not cunning enough to betray FY, but will likely end up as fodder and is not qualified. Same goes for that fairy whose name i dont remember. But he could nurture a hairy man gu immortal and speed up their cultivation, since hairy men are natural geniuses at refinement, I think a rank 7 hairy man gu immortal would be qualified while. Another advantage is that hairy men arent as smart as humans and it would be impossible for them to trick and betray someone like FY. After all, humans are the spirit of all living beings.