Making Mayo by hand , using whisk , emulsion breaks down
It's important to determine whether your emulsion actually broke immediately or was just creaming.

I'm going to trot out this diagram again from yesterday:



(source: Cube Cola)

Creaming occurs when the oil drops, which are less dense than the water, float to the top.  As long as the droplets don't coalesce, you can still fix this with agitation (whisk, blend, or shake vigorously).

Emulsions with coarse particles (of oil) are much more prone to creaming, because their increased buoyancy makes them more able to push up past the water molecules.  You want to have a very fine "mist" of oil suspended in the water; if you were using a squeeze bottle, perhaps the individual drops were simply too large.  A ketchup bottle in particular would not be appropriate for this sort of thing, you'd want to use something closer to a syringe (or just get an actual syringe).

Now if you keep adding oil to a creamed emulsion or let it sit too long then it will also start to coalesce, and coalescence and creaming together are what cause an emulsion to break completely.  This, you really can't recover from, except to let it separate completely, skim off the fat, and start over.

So, to recap:


Your oil drops may have been too large;
You may not have been agitating enough, especially when it started to cream;
You may have added too much oil after creaming had already started.


I also agree with commenter Henrik that the amount of oil sounds a little high; 3/4 cup would be more reasonable for 1 egg yolk.  But since you say you only got 1/3 of the way through, that's clearly not your problem here.