Christmas has never been what "they" try to make it, whoever "they" are - it's about what's in your heart.
People who only know my situation worry about me, if they care at all. People who know me don't worry that much. I have no siblings or children, and both of my parents are gone. The first Christmas after my Mom died, I spent in Korea. My Jewish boss had everyone over for Christmas dinner. I had a great time. Since then, I've usually spent Christmas with friends. One year, I served meals at a Salvation Army shelter in downtown Washington DC. The neatest thing that happened there was when a woman from the Salvation Army sat herself down at a piano and began to sing "Stand By Me" and many folks joined in. I have spent Christmases alone at home, sometimes feeling sorry for myself. At some point, I usually realize I'm making things worse by thinking about things I lost or will never have.
My advice, to be taken with a grain of salt is:
1) Christmas has never been about what "they" try to make it. "They" can be merchants, friends, family, or co-workers. For some, it's a religious holiday, for some a gathering of friends and/or family, and for some it's just another day.
2) Don't feel guilty for not being thrilled to pieces about it if you aren't.
3) Do something. If you're alone, cook yourself a great meal, go for a walk, call someone on the phone, rent a movie, go help at serving meals somewhere, play music at a hospital, nursing home, or shelter...etc
4) If someone invites you to spend the day with them - GO!