How to mourn?

I found out this week that my Grandfather had passed away. As soon as I heard it I started to cry. Anyone who knows me at all knows that I don't just cry about anything. You could be saying to yourself right now "my goodness this is her Grandfather who died she should be crying"
Well you have to understand why I was crying.
Growing up I only saw my Grandpa a handful of times and the last time being when I was about 15 or 16.
I was not allowed to have a relationship with him because of my step-grandma and how much she did not like his kids or even his grandkids.
So for all of those years when most grandkids enjoyed going and spending time with their grandparents I did not.
I did not have sleep over’s, summer stays, I did not even get slipped candy by my grandfather.
The few times I do remember him are hard for me because I'm not sure if they are my memories or just ones that I had made from something someone had told me about him.
So how do you mourn for someone that you did not even know?
The reason I was crying is because I would never get the chance to know him and my children will never get the chance to even meet him!
Take your kids and your grandkids and even your great grand kids and love them and spend time with them. Because you never know when you won’t be able to anymore!
Not only did I not get to spend time with my grandfather before he died but my step grandmother is not letting the family come to the funeral.
How do you mourn for a grandfather you never knew?
Its hard let me tell you, because there is love there for him and now I will never get to show it to him!