It's awful, especially when it's a mate rather than family. If it's close family, people expect you to be upset, when it's a mate, you feel as if you have to be strong for the family, when inside you're torn up, and probably could do with lots of support yourself. When it's a younger friend, sometimes another seperate wake away from his family is the best way to remember the friend that you knew - who may be very different from the brother/father/responsible family man that his family knew.
It generally gets better with time, although there is no right amount of time to grieve for, and indeed no right or wrong way to grieve. If things don't move on CRUSE bereavement counselling can be helpful although are a bit hit and miss. Sometimes an event like this can precipitate an episode of depression, something to keep an eye out for, but be wary of anyone who suggests antidepressants without exploring other avenues.