Have the same story…
I suppose my first riding partner loss was my wife. As we started having kids she had less and less interest in riding. By the time my oldest was 6 she had lost her seat on the tandem.
It started, in earnest, in my late 40’s when it was hard to keep up with the club rides. At that time, I would ride to the ride starting point solo and stick with the pack as long as possible and then ride home solo. That way I got to visit with my riding buddies for a while. On one of those solo rides I fell on a wet bridge deck and bunged up my wrist. I managed to ride 12 miles home one handed. That incident put an end to that solo ride to the club ride program. (I was about 51-53 at that time.)
A few other guys and gals in our 50’s would meet to ride once a week. However health issues, retirement and reduction in bike interest caused that group to melt away over a 10 year period.
In my 60’s I started doing more of the club “social rides” also. However the social rides made me a little grumpy because of the slow speed, frequent stops the low rider skills and the tendency to follow the same routes week after week.
I have always done more solo riding than most of my riding friends. I am lucky to live in farm country and no matter which way I go from my driveway it is a good ride. So at age 68 I tend to ride long slow solo rides tough farm country about 90% of the time. . I am OK with that too. (This summer I took the train to Denver and then rode 200 miles around Colorado to my 50th high school reunion, solo.) Sadly, some of my best riding buddies just can’t do it anymore. I guess I should count my blessings.