I'd cancel the date, and, not go into too many details with the guy about why...just tell him you have a friend in need. Tell him how badly you feel about cancelling, but, that she's a good friend. But, I guess I'm not understanding completely, you'd have to miss the date because your friend would be alone at your house? Would that be such a bad thing? Or is she staying at your house and you are going to talk with her and be with her? I just wasn't totally clear...