Oh, I'm so very sorry!!! I wish there was something I could do!!! This may sound self serving: but maybe if you read my love poem to God: "To My Father", you'll find some solace and inspiration. I don't know the details but maybe your grandfather's cancer is survivable.
Love, Chris
Go cry to your date.
See what he's made of.
If a girl had a good reason (as you do) I welcomed the chance to make her feel better.
If he doesn't feel that way, well, fuck him (not literally) and find one of your girls.
But a real man would totally have your back, even if you're new to each other.
Love, Chris