One will never be able to make others understand so don't bother yourself trying. Those who truly care about you will accept your grief as genuine. Make sure you have someone to talk to about your feelings. Getting them out in the open is the first step to healing. Share funny moments and poinant memories that will warm your heart and make you smile.
Remembrance is a wonderful thing.
Keep momentoes of your cherished friend. Put out cute photos or keep their favorite toy somewhere where you might see it and think of a fond memory. Try to continue with your activities because isolating yourself will only make you more miserable. Find resources to help you deal with the pain. Read books, browse for help on the web or if you feel that you need to talk to a counselor.