Hi and welcome mliacm;
You've answered your own question hun; you just needed to talk. We all do now and then - let the pain and confusion out and give it a voice. That's how it works and you've done famously.
It seems to me your grief began a long time ago when your grandpa started getting sick. When we're young we don't have experience with grief or the prospect of losing a loved one so close to our hearts.
Sometimes, our emotions will turn off to save us from enormous emotional pain. It happens like this because our brains know exactly what we can take or not. Feeling nothing's a result of this. It's a normal brain chemical response.
Gradually you'll begin to 'feel' something unless you purposely avoid it. When I was 15 my nanna died. I cried deeply for a long time, but could never say her name without falling to pieces.
I didn't face my true feelings about that until I was in my 30's. I was so angry with her for leaving me alone with my hostile parents. But, the 'shame' of feeling that way kept me from dealing with it. It had gone so deep into my psyche, I'd forgotten. But my body/mind knew it was there which caused my inability to talk about her.
What I did, was write her a letter. (in my own hand) It was awkward to begin with; you know, "Hope you're ok, what's it like there?" sort of stuff. But then the truth started to flow from my hand. Eventually I was ripping pages with the pen as if it were a knife!
I was so angry with her! That anger's absolutely appropriate considering our circumstances. She was my light, my love and my safety; she was my all...
She left me alone and I hated her for it. Once the words and yes screaming, came out of me, a shift occurred. I could say her name and talk about her without feeling emotional. I got out the poison that was keeping me down.
Honesty's the best policy when it comes to grief. When you're ready, and that could be months or yrs from now, sit quietly alone in a safe environment and talk with him. Tell him your innermost thoughts and pain. Cry, yell or feel whatever it is that's necessary to get it out. Write if you want, just talk to him.
I hope I've helped hun. It's a very personal journey...you can vent here anytime you want ok.