I thought you broke up with her a cpl weeks ago in the middle of the night.
If you're serious - you find out which type she has & how serious the situation is. You decide whether you stay & help or run. (You'll stay.) You become as supporting & hopeful as you can be, & try to see her through it in a positive, upbeat manner, with good humor. Keep her laughing for as long as she can breathe. You do NOT get all maudlin & "remember the good times" with her. You help her to live life as best you can within the parameters of her physical abilities, keep her mind off the subject as much as possible, & make her laugh & enjoy life with each & every breath she has. If you are going to help her, you should learn to be the funniest guy around her, with upbeat jokes & pratfalls & goofiness. (Yes, it's perfectly okay to joke about the disease as well as it progresses, if you can make jokes about it that make her laugh!) It'll help you get through it, as well, with good memories for the two of you if she survives it, & & you'll feel better about yourself & her if she doesn't. It takes the sting out of the "shoulda-woulda-coulda's" too. That's a tough one, Ryan, but they tell you God doesn't give you anything you can't handle.
That's the best advice I could give anyone in that situation. I'll say a prayer for ya, Ryan, but I have the feeling that you'll do the right thing as long as you can keep your cynicism & lack of faith to an absolute minimum. That has no place in your life with her as she goes through this.
I wish I'd had it in me to do that for my mom when she had it, but I didn't know how. Then again, I was only 19 when she died from the chemo they overloaded her with, & dumb as a box of rocks.