@VINT64 Well elves in actual myths can be tricked into counting things endlessly, it's apparently a valid defense against fae to have a jar full of beans at hand to toss on the ground, if they come after you.
So he lied about needing immortality spell, although it is somewhat true he wanted it but it is for before the girl can learn to be independent. He just want her to stay and teach his disciple until his disciple can join her.
This is really a sad story, what a genius author T-T