Ending

He saved her life, would she have not been able to explain to the authorities about the whole situation?

She wanted him to go away for her (and her son's) safety, rather than Rabbit's.

If you were in her shoes, I'd imagine you would do the same.

You have 2 options;
Tell your son that his father was killed by a stranger.
Tell your son that his father was killed by his first son, that he sent off to his serial killer uncle to be killed with his aunt.

SPOILER ALERT: I hated the ending. If the dad was so desperate to get rid of his wife and son, why would he remarry and have ANOTHER son? I understand that some people fall out of love and hate their spouses, others just want to live a single life, but if you can't even love your own son, why have any other kids? What's the difference? And how did he even know his brother was a serial killer? It would have been way better without the last minute twist.
I assumed the new wife's plan was to say someone broke into their home and killed her husband, and pretend it was a stranger to protect Rabbit and also her own son.

The ending was very sloppy in my opinion. Brad was obviously a terrible person and he is clearly the aggressor in the conflict. Any court of law would rule Rabbit innocent. Why the wife instantly made up a lie about burglars is completely unnecessary. Maybe she was protecting Rabbit? Doesn't matter. He's not going to last long on his own anyway. Can't pay bills, get supplies, etc. No shred of hope in this ending, which is usually OK in a horror, but this was building towards his redemption the whole movie and it just didn't happen.

The film should have ended with A.) He overcomes and turns into a normal person. or B.) He himself becomes a serial killer. Instead we got this.