I am feeling very sad

As his mother reached her 100s he's probably going to be an older person, 60 at youngest. Sudden events overtake people all the time.
OP I don't think you should take your friend's silence personally, it seems unlikely to be directed at you in any way.
Yesterday I had a phone call from someone with whom I'd not been in touch since the 1980s. We talked for an hour and there was no significant reason for having been out of touch, our lives had just drifted apart.

PrintMiss I would suggest writing a letter to SSD saying you are an old friend and are worried about him and have not seen him for ages.

Make it quite clear to SSD that you do not want them to give you any information about his circumstances, but that if they do know where he is would they be prepared to forward him a letter from you.

That would be leaving it entirely up to the man himself to decide if he wants to see you. with the possibilty of no response to you. That could be done by 3rd party contact.

Hopefully an SSD would look at doing that confidentially and sensitively. Who knows these days?

I have done that and the woman in residential care was very pleased to have regained contact with her friend. Preventing social isolation was my "excuse" .

Perhaps your friend feel as I do . We have old neighbours whom we lived beside 48 years ago . They have always done the keeping in touch and we have visited on some occasions over the years. Last year I decided not to send a card and got none from them but had a letter from them in the summer which I ignored. At Christmas we had a card asking if we would like to visit . Terrible of me but I just ignored it as well . They are older than us and frailer and I prefer to remember then as were all were in the past. What would have in common anyway apart from the children 48 years on . Some people just do not want to keep in touch .

I have been widowed twice. My first husband died of bowel cancer, aged 44; my second husband died 2 years ago of a rare form of early-onset dementia. There is a period of time after your loss when you are just trying to get on with it and meeting old friends, who naturally have their own feelings about what has happened, is all too much! I dreaded those well-meant hugs and 'How ARE yous'! I needed a bit of space to get my act together. It was very difficult, for example, to go to my colleague's retirement do a few months ago, where everyone (my former colleagues) knew that my husband had died. Give the guy a bit of space and then, if you do manage to get back in touch, try to make sure you have your emotions under control.

Thank you everyone for these suggestions and comfort. We cannot visit our friend we left the area and are now not able to travel that far. I agree that he may have depression, or died, but quite honestly I know the family well enough to know that they would let us all (there is a circle of friends here), know. I am bewildered and just hope that he has not declined into dementia, or has some awful illness and does not want us to know for reasons of his own.
That would be a really awful thing to happen because we were always so close and supported each other.

I've just seen this thread PRINTMISS and hope you feel a bit happier today.