We'd do the same thing if we were Edward Norton.
So Tyler never existed: He was a personality the narrator invented to escape his depressing middle class life. Strangely, when this all comes out, the narrator seems to handle it rather well for a man who previously had a nervous breakdown over Ikea furniture. It's almost like he's experienced something like this before ...
And he has, according to one popular theory, which states that the narrator is actually a grown-up Calvin from Calvin & Hobbes ... which would mean Tyler is Hobbes.
Or at the very least he skinned Hobbes.
For those of you who grew up in a Mexican prison, Calvin & Hobbes charts the adventures of a young boy and his best friend, a talking tiger who looks like a stuffed doll to everyone else. But other than the fact that both Fight Club's narrator and Calvin have imaginary friends, what else could they possibly have in common?
Well, first, there's the fact that they both tend to show up with inexplicable bruises all over their bodies -- when Calvin imagines a fight with Hobbes, his parents can see the bruises afterwards, so it's obvious that the kid likes punching himself and blaming it on his nonexistent friend. Just like Fight Club's narrator (whose name we never learn).