Why does a woman, while in a relationship, get "comfortable", stops having sex or at least the sex dwindles, doesn't take care of her appearance etc. The guy cheats and then she goes off and "glows" up starts dressing better again, taking care of herself, showing how happy she is without him, all the things that if she would have kept up while in the relationship may never have caused the guy to stray (all hypothetically)

How are women not able to see this? Ironically many will go through that, get back in a relationship and the process starts all over again. How does this happen?