wasn't he supposed to be with the old grandpa when he talked about cultivation with her? 😮‍💨 it's been awhile, but I am sure that was the case

Found it - she had ~30 years life left near the beginning, and needed to sleep with someone, preferably with 'light in their heart', passed the Spirit Treasury realm (I think, which Xu Qing just finished) to increase her lifespan. Pretty sure Er Gen didn't forget, and her talk when leaving his mansion is related to it.

so, it's been about 1000 chapters - but wasn't there something to gain by sleeping with the fairy? or she was on a few years time limit to sleep with someone with 'light' or she'd have troubles. xu qing wouldn't be strong enough in time...blah blah. that guy that was turned into a candle a hundred or two chapters ago was really after her too. may have to go back & read if no one can help me remember. wondering if author forgot, or if it's coming back soon.

I'm withdrawing from lack of chapter