What would you do?

[Karen]

I'd reschedule the date, making clear that this is no reflection on him. Something really has come up, and a friend needs you, but explain you were looking forward to the date, and are not brushing him off.

"Gotta help a friend" is sadly an oft-used excuse, but in this case it is true!

[Laura's Babies]

I agree with Karen... But if it is that you want to cancell because she will be at your house... she might just like some alone time to think.

[JenBKR]

I agree with the others, I would probably explain that something came up, a friend is in need, but you are really looking forward to your next date with him. I bet he'll be understanding about it.