It seems to me as if this incident has knocked your confidence Jeannie, understandable, but from reading your post it sounds as if it was a bit of a one-off. You say none of the ladies you get on well with were there - this means that you do have friends within the group, but they didnt happen to be around. You then go on to mention your family issue, and then to a much bigger fear of being on your own if your partner should cease to be around. It sounds like one of these accumulating situations where one incident on its own wouldnt have meant much, but together they have led you to worry about having friends and support into the future.
From my experience getting left out of group chats is sometimes just random and no reflection on you as a person. I went to a Pilates class for about a year before anyone even spoke to me, yet in the New Year I joined a different Yoga class and was drawn into the well established group immediately. I havent had a personality change, nor was I making any special effort. I think the group dynamics are just different, so please dont take it personally.
As to the longer term issue of potentially being left on your own, I do think that is something you might be able to address now by joining some new groups who may well be more friendly. Even if you dont like that idea, its never too late. My next door neighbours husband got dementia when they were both in their 80s. They had pretty much kept themselves to themselves, being friendly but quiet, but she invited all the near neighbours round to a tea party one Sunday afternoon, explained the situation and asked for help. Lo and behold an entire support group sprang up and continues to function six years later. People can be astonishingly kind, helpful and supportive even to virtual strangers, but sometimes I think it just needs something to break the ice.