Not a grandson, but my youngest son killed himself on December 12th 2008, aged 19, we are coming up to 3 years soon.
It is hard, it it so bloody hard, I think of him every day, and go through periods of having very vivid dreams, some totally disturbing, some that are actually comforting, but it is hard to explain.
I'm sure it was hard on my mother (his grandma) too, but as she hadn't spoken to me for sometime before his death,and saw no reason to change things after, even though I tried (I thought if anything would heal the rift,it would be that, but no.), I am not in a position to say how the loss of a grandson feels.
I would say however, that I found some comfort at the time from reading the things that his friends had posted on a special facebook "wall" that they set up. (I don't acually do facebook, but made an exception). They had all posted the crazy things that he had done that made them laugh, and I must say they gave me an insight into other aspects of him, and saw how much he was loved and valued by his peers.
When I see ds1, now 33 (there was a 10 year gap between them) we do talk about J, and how funny he was etc. when the natural flow of conversation leads that way.
With regard to advice, all I can say is DON'T avoid mentioning your grandson, talk about him where appropriate, acknowledge the loss, but focus on the good/happy/funny things.
With regard to counselling oranisations etc, there is Families In Grief, but my wonderful GP (who was brilliant and has continued to be) warned that sometimes people in these organisations can almost "feed" their own emotions through the work they do with others. (Maybe I haven't put that very well)
There was a poem that we included in J's order of service that I think sort of hits the spot.
I am a bit of a techno numpty, but I will try to find it and if I do I will C&P it.
Much love to you all.