SPOILERS ALERT, at the end, when she returns...
... to Ben Affleck's character, after, spoiler alert, killing that man, do you think they will live happily ever after together and that Ben Affleck's character can live with Amy Dunn for the rest of his life and that she will never double cross him or worse try to stab him and kill him or anything like that?
Besides, do you think she has reformed when she returned to him and that at no point whatsoever will she try and do anything similarly bad to anyone at all, save for maybe (not to imply say a movie "Return to Sender" is a continuation to this) someone who tries to hurt her and in self defense only?
And do you think he has forgiven her and has the right to do so? Granted, there are many bad, evil and downright abusive men in the world out there with no conscience who sadly hurt women a lot, but Ben Affleck's character seems to be a normal guy, do you think that he will treat her with respect as well and that also, if Amy Dunn does NOT at any point get arrested or anything for whatever wrong she did in the movie, she has nothing to worry about and Affleck's friends and relatives must meet and greet her with open arms?
Or maybe she might become somewhat similar to that abusive wife character in the made for TV drama "Men Don't Tell" (1993) with Peter Strauss and constantly hit him and whatnot but he will gradually be forgiven until she ends up in a hospital or something and he can prove to the police it was her who started it and then they get a divorce but maybe she'll learn her lesson and become a better person without prison time or even mental hospital treatment, and also because she is attractive, maybe Ben Affleck's character could at least feel asthetically pleased for loving a girl who had good looks, despite whatever trouble she brought or potentially brought him, if he doesn't get killed by her that is.
Who knows?