Why Do All the Immortal Maidens Scheme My Corruption?

(Reverse NTR, QCQS) Lin Que has a devoted Dao companion, Qin Wanyan, who is wholeheartedly dedicated to him. He thought life would continue peacefully and happily like this forever.
However, one day, three letters appeared on his desk.
Opening the first letter.
His former senior sister, who had once imprisoned him and left him with deep psychological scars—a cold and obsessive yandere—wrote in a calm tone:
“It’s fine, Wanyan won’t find out.”
Opening the second letter.
His Dao companion’s master, the dignified woman he also respectfully calls teacher, revealed an extremely contrasting side:
“Queer, you wouldn’t want your Dao companion to lose her status as a direct disciple, would you?”
The most deadly was the last letter, written by his sharp-tongued sister-in-law:
“If brother-in-law doesn’t want sister to discover these things, come to my room tonight at midnight…”
He clearly just wanted to live a peaceful life with his Dao companion, so why did things turn out this way?
————
Main wife Qin Wanyan: “Even if I must wear a green hat and let Lord Lin take new concubines into his harem, as long as I don’t die, you all will ultimately remain mere concubines! At the peak of immortality, proud in this world, where there is Wanyan, there is heaven! Reviving the glory of pure love is our generation’s duty!”
However, after some time…
Qin Wanyan: “I’ve learned to behave, please spare me.”