Hi David,
I used to feel alone all the time, but now I feel better because I have more than enough to occupy my mind, work, study, friends etc. But still, I think I can really understand the kind of state you are in right now. There was a short period in my life in which I was unable to have normal social contacts to the outside world. It was a new place for me to be and I didn't have any friends there. I think that might be what worsen my depression. I was so upset and stressed all the time during that period. It was hard, and just like you, I couldn't see how I was gonna get out of it.
I think to adjust yourself to the new life after retirement is probably not easy to do... Sometimes I really feel there's really very little we can accomplish in each day, even for us younger people, sometimes I find it very boring on weekend days when I am being a little lazy and want to do nothing. I don't know, do you think you could try something new, and easy to do at home? Like do a little gardening, cooking, reading books, or maybe try to write a book... Just try to find as much as distractions, I think you may feel a little better when you feel there are more to accomplish
I hope you are feeling better

Take care...
Best,
Toni
[i] What our mind can conceive and believe, it will achieve.