How to move on after the death of a loved one
Both my mom and one of my closest friends died in 2003, and it took me awhile to stop being angry and grieving on a pretty much constant basis.
To begin with, I was shocked and hurt at their deaths. The shock lasted several months in my case, due to the manner in which each of them died.
When grief came, it hit hard. I would break down crying at simple, everyday things - the card aisle in the store, stacked with Mother's Day cards; or a song on the radio that we'd had a private joke about. Sometimes I would run into people who didn't know about the death, but had known one of them casually. They would ask after her, and the painful explanations would follow.
Now it's 2008. Five years have passed, and I am accustomed to their absence.
The only real answer I can give you is: time. You will grieve, you must grieve. But go on living your life, doing all the things that need to be done. Try to go out with your friends - eventually the pantomimed motions of enjoyment will become real.
Remember that you are not dishonoring their memory by smiling or laughing and continuing on. If they loved you, then they wanted you to be happy. It will always hurt a little when you think of them, when you look at your life and see what they have missed. This is part of human growth.
Trust me, you don't want to "get over" the death of a loved one. That would be tantamount to forgetting them. You want to honor their memory by continuing with a rich and full life that they would be proud of.