I grieve for my loved ones not because i want to, i just do, i feel sad because of all the experiences we might have had together will now be lost forever. I never get the chance to tell them everything i wanted. I won't get to laugh with them, tell jokes with them, spend time with them. It reminds me of my own impending death, and that the older i live, the more loved ones i will have to watch leave my life forever.
I grieve for the people i was very close to, because i will miss them. It passes more quickly for some, and less quickly for others depending on how close i was with them.
No one knows what happens when you die, find someone who does, and you'll find a liar.