Oh hunny, I am so sorry. My grandma was my best friend. She was the mother figure my own mother couldn't be. She was my everything. Cancer stole her from me. She was diagnosed in January, and was gone by April. The only thing she ever wanted to see me do was be a mother, and I lost her when I was 4 months pregnant with my first child.
To this day I miss her terribly, and in a few weeks I am getting a tattoo for her.
I lost her to breast cancer. The same cancer she had beaten twice before. The third time she just didn't have the fight left. I was SO angry at god, the world, the universe, the doctors, everyone.
Between now and 'when ever', don't cry. Just enjoy his presence, hold onto the hugs for a minute longer, make sure you tell him anything you want before he goes, and ask him to think of a sign he can give you after he has passed to let you know he is still around. My grandma touches my hair. When I need her, my hair tingles. That is her. We agreed on it before she left because that is what her mother did to her.
If you ever need to talk I am here hunny. PM me here, send me a message on FB, I'll give you my email. I know the hurt you are going through now, and what will follow. I am SO, so very sorry.