Oh well, I can't really even speculate on what their relationship was other than it was apparently volatile, if they argued so much he had to take her home and she actually jumped out of his car before she got home.
As for if the party was at HER apartment or if they went to another party somewhere else, I agree with you that the reporting makes it confusing. But somehow, things that have been said, what I've read, leads me to believe it was at her apartment. That's the party I believe the news is referring to.
And GGE just said it....he waited nearly 24 hours and didn't look for her or check on her well being. Even if they were just casual friends I would think you would at least call....
But then on the other hand he might have still been angry with her and didn't give a damn! grrrrrr