writing with no end

I have a rule. I never start a short story until I know how it ends. This is because I have many wonderful starts to short stories which have no ends. Such as:

The Deadsquad Grays saluted us: wary, new-made soldiers boarding a transport on the windy tarmac in Montana. The Grays amounted to the home front of the Endwar, rusted-out men who boxed-and-shipped the ash of our casualties.

and

When I started investigating the unexplained deaths of vampires at the Denver Coven, I never would have guessed that the murderer was me.

But I've never had a character change the rules on me midstream--not in a short story, that is. Like in the current WIP. 2500 words flowed like boiling butter and then slid to a screaming halt at:

“You probably want to know what happened,” he says. “Why I left.”

He blinks some more, finds my face. I hate him looking at me, seeing me like this, old, and all worn out. Parts of me flake off inside, memories thaw. My fingers tighten on the gun. Thank God the gin has steadied my hand.

“No,” I say. “I don’t.”

And that's all she wrote, folks.
Literally.

Fuck.