Well, here's what I see. I don't believe it to be the alternator either.
If, by removing the relay and jumping the two terminals, you get fuel....don't you think that the relay is the issue and not the ECU? The ECU isn't the endgame, it's the mediator, the middle man to most systems.

 

thats why i asked him how he started it. most of the jumper boxes ive ever used are **** and loose there charge before you can even start the car. so i figured if the car started and ran when it was hooked to another car then it was the alternator, but thats not the case apparently

 

From what i understand it wont start, it just cranks over slow and the lights only dim.
It could be the alternator, if its locked up .. 3 weeks of sitting shouldnt hurt anything unless it froze up and the water pump cant turn.

 

Oddly, I had this same type of problem... you dont happen to have a (highly amplified) system in that car, do you?

 

With mine, I was running two 1k watt amps with no caps... eventually it ate up the alternator... which still worked but wouldnt charge the batt. correctly, and didnt power the car right at all... I may be way off... but the conditions seem rather similiar (as Im in MD right now, where its like 40 degrees in the sun) I ended up replaceing the alt. and batt, everything worked fine then... (P.S.- I bought a few caps this time too, lol.)