Not quite the same situation but when I faced Christmas by myself for the first time I hated it. Everyone else had family and loved ones to spend it with and the images of people gathered round the tree, exchanging presents or the big Christmas dinner full of joy and laughter that I saw on TV made me feel even more alone. I actually love Christmas, it's by far and away my favourite time of year and I felt I'd lost something very special to me. That was a very difficult year.
I quickly adapted though, I realised I could still make Christmas special to me by making new traditions. I could also be a bit more selfish which goes against the spirit of the season but I can do the things that I want to do and either do them by myself or find others to share it with.
So the second year I made plans to go to the Panto with a friend in a city away from home, the third year we even made a weekend of it and booked a hotel room so we could take our time and enjoy the Christmas atmosphere. I now do this every year, somewhere new if we can or more local if money is tight. I also do it as close to Christmas as I can so I have something to look forward to.
I would still put up my tree and deck the halls so to speak, I go to John Lewis every year and buy one new "fancy" glass ornament to add to the tree, this year will be the 15th. I'd also buy my Advent calendar, I've tried coffee ones, hot chocolate ones, skin care, beauty, alcohol, jigsaws, scented candles etc....just for the fun of it. I purposefully do this by myself so I can take my sweet time deciding what to get, hot chocolate in Starbucks with a mince pie, wonder around the shops looking at sparkly things.....Joy, I'd have something planned for most weekends from mid november onwards and I'm not talking about huge events, meeting a friend for coffee or a bite to eat gave me something to do.
Christmas morning I would wake up, crank up the heating, make myself a hot breakfast, pop open the Bucks Fizz (no judgement please), watch the Snowman and relive the childhood memories and freely sing along to "Walking in the Air". Shower, dress, go for a morning walk if it's not raining, wish everyone I see a "Merry Christmas". Go home, call family, make dinner, watch a film and snuggle down. It's actually a very boring day from the outside but I love it.
Things changed when I met my partner but for those years I was alone I made Christmas special to me again.
I guess what I'm saying is, make the day what you want it to be, it doesn't have to be a huge family event. Reach out to friends or family who might be spending the day alone and see if they want company or plan the day around you. A few more years and the grand children will appear and your son and his partner will be banging at your door begging you to host Christmas!!!!