UNLOVEtale is an au where every monster in the unground's manners are quiet nicer and their clothes are pink. Sans has fixed the core multiple times..

..you've heard this all before, haven't you, partner?

let me tell you a NEW STORY

Sans wasn't able to fix the core again. He was too weak. The entirety of the underground shut out sans.. sans was worried his wife and kids would, too.. he couldn't save them now. Maybe they, too, would hate him as much as the rest of the monsters