RocknRoll I'm so sorry to hear how anxious and upset you are feeling at the moment. I think many people, as they get older, think about some of the things they have missed or are missing. Of course, there are always those who have fantastically full lives - with lots of friends, social events and holidays - but I think they are probably in the minority.
Don't imagine that everybody with partners and families and relatively good health are idyllically happy. It is very possible to, at times, feel regretful, sad, alone and unfulfilled, even when everything seems to be in place to ensure a happy life.
I think probably your health issue is exacerbating your anxiety and depression. It is quite understandable that your illness is making it much harder for you to appreciate the good things in your life - your own creative business which presumably you enjoy, the companionship of your dogs and seeing your daughter frequently. (As for grandchildren, as they get older it does seem that grandparents (and even parents) see less and less of them).
But there seem to be some things that you would like to do that you feel you can't do. But perhaps you can. Take holidays, for instance. I believe there are several organisations that run singles holidays and it might be worth doing some research as to whether any of these organisations might suit your needs and your pocket. There are also people who will look after your dogs for you in their own homes, if you are worried about leaving them in kennels.
If you feel a holiday would be too much to undertake at the moment, I would imagine there are local activities that might be of interest to you - choirs, art classes, WEA courses, U3A groups, book groups, the WI, Townswomen's Guilds, etc, etc. I too can feel quite down at times and I think it is important at such times to force myself to keep active, to do something that interests and occupies me, and to mix with people even when I'm feeling low.
I do hope some of the advice given on this thread is of help to you and that you soon feel better.