I'm imagining this complaint from the other side:
I was going drive my boyfriend and his buddy to Chicago in my Corolla, but school obligations came up and can't, so they have to find their own way to go. They still want to take my car though, even though its not theirs. His friend's gf offered to let me use her car while they're gone, but no thanks, this is my car and I don't need the extra wear and tear when there are other cars available.
Why, exactly, can't you take your gf's jetta?