i'm sorry the ign switch didn't solve your problem. It certainly was a plausible cause.
I thinkt the radiator fan normally runs even after the engine has been shut off, until the coolant temperature sensor says the coolant has cooled down enough. The power gets fed directly from the battery via a relay. If the temperature switch goes bad and "hangs", it will cause the fan to turn at all times, even with the key removed from the ignition. You should hear it run though?
The fan could be seized or otherwise inoperational, yet still drawing power when the motor is trying to turn. You would have heard the fan run if it was running and the engine was not.
You should charge the battery with a wall charger before jump starting the car. Modern alternators aren't designed to charge a near empty battery repeatedly, it's too much to ask. They may overload. They're good for maintaining a charge, which is what their main job is anyway. You can also charge the battery with the jumper cables, allow it to charge for 20 minutes at least before trying to jump start. There needs to be some life left in the battery. Jumper cables are often not thick enough to carry full current to the battery to run the starter and everything else in full power.
Try again with a fully charged battery, see if it starts and runs. I know you tried to charge the battery at least a little bitr before with no luck. Then you can continue tracking down the root cause of the drain. Inspect the radiator fan, see how it works. If you let the car sit at idla after a longer drive, the fan would probably come on after a while, and then it should turn off again. If this cycle works as described, then I don't know how there could be a draw on that fuse. Stuck radiator fan relay maybe?
What exactly happens when the battery HAS power, and the engine still won't start?
Does the starter turn the motor over at all? Does it just click, or does it seem that no power at all is going to the starter? (no clicking)
I'll Opt Out to allow other experts to offer their assistance, in case someone knows more things to check.