Psychopaths cannot change.

Psychopathy is incurable and untreatable. They do not want help, because they believe themselves to be superior to "regular" human beings. You do not have to worry that they're a changed man or woman, because they're not. They may give off the illusion of "goodness" in order to maintain an image of normalcy, but like anything else with a psychopath, it's all manufactured. They are incapable of seeing other human beings as unique individuals deserving of love & kindness. All they see is pawns on a chess board. Someone who is capable of abusing you (with silence, gas-lighting, cheating, and pathological lying) is not also capable of suddenly being a decent human being because they found a better partner. These qualities & behaviors are indicative of a serious personality disorder, not temporary symptoms a bad relationship.