I agree with many of the answers here. It appears as though people forget our grief because the pain of the event is still so strong to us. We think, "how can life go on when "x" has just happened"? How can anyone be happy? I think there are different levels of people around us that hopefully will be there for us at different depths. Our family should be the ones to stick by us the longest and give us the support we need to go through the grief process. They should be the ones to help us handle our more significant feelings, emotions, and specific personal needs during the crisis and thereafter. Our closest friends will be there for us longer than surface friends. Hopefully each person has a few really close friends that can help us walk through the process. These are the people that don't have a problem asking what you need, just sitting and listening, etc. Finally, our surface friends and acquaintences may acknowledge the occurrance, send a card, etc, but may go no further than that. It's not necessarily that they forget the event that occurred, but they don't have the same emotional investment in your life that your best friends and family do.
It is definately important to make sure that there are people around that know you are still suffering and that you need help in dealing with the tragedy. If you appear to be doing well, putting on a good front, others will feel you are doing better than you are. It's OK to ask for help.