Grief, when does the sadness end?

One of my favorite people just passed away unexpectedly. I find myself walking around in a fog and waking up in the morning saying, “I just had the most horrible dream.” I get out of bed and realize that it wasn’t a dream and my sister-in-law, my friend, is really gone. I just feel so sad. I try to think of the good times and the fun we had but the sadness just creeps back in with the reality. Any suggestions on how to cope?