Teresa,
Everyone responds to this disease differently. I have to tell you that many of the folks who appear so strong now, were in the same position when the diagnosis was new. It is overwhelming and terrifying and you can't see any other scenario but the scariest one.
But it gets better as you learn what you are dealing with and have a treatment plan. You learn a "new normal."
It might also help to try to focus on every day you have with your father as a gift. Instead of focusing on how little time you might have left, consider each new day as a gift to be enjoyed and thankful for. That sounds kind of hokey I know, but he is here and with you now. And if you spend this time fretting about what may happen in the future (and let's face it, none of us is guaranteed tomorrow), you will miss some valuable time just being with your Dad.
We'll be here to help you through it.
Susan