Melisande in Kushiel Legacy.
The grooming, slavery, gaslighting, raping, stated that she has no conscience, she murders the mc step father and brother, starts a civil war, her best friend is banished to a remote island for a decade etc. And the MC is still obssessed with this psychopath after 6 books and over 30 years later sniffing her letters - there is no development in the relationship. Melisande gets no come uppance or face any lasting consequences for all she has done. Instead its retconned in the second trilogy that she actually the good guy and saves the world.
Imriel, Melisandes son is the mc of the second trilogy, which takes place a couple of years after the first trilogy.
Phedre and Joscelin gets mind controlled into antagonists by the real villain. All of Melisandes past crimes are pardoned and is regarded as a hero, even though she never had any come uppance or prison. She always had power and influential within the church, is in a happy relationship, gets to reunite with her son and together they save Phedre, Joscelin and the world.