Meow,
I think the protagonist is the serial killer having dual personality and its nightmares are part of blured dream memories he remember of when his other side is controlling his body or his other side trying to get ride of him in his head to take control in those dream fights.
At least some of them.
In worse case the end since that a terror story would be...
He killing the protagonist boyfriend in the end of the story and when he back to his normally personality the protagonist remember what happened suicide to put a end in the murders.
Maybe reading Echo really fucked my mind to much.