In Fight Club (1999), Narrator looks down the barrel of a gun that's been stuck in his mouth. The gun is held by a man named Tyler:
Narrator: For a second, I forget about Tyler's controlled demolition thing and I wonder how clean that gun is.
Tyler: It's getting exciting now.
Narrator: That old saying, how you always hurt the one you love, well, it works both ways.
What "both ways" is Narrator referring to?