Watching who is still in your life explains most of this
The names have barely changed in twenty years. A Taurus Moon in the 11th house forms friendships slowly and then keeps them permanently, so your circle is small, old and unusually solid, and the people in it are effectively part of the structure of your life.
What that gives a group is ballast. Where others come and go, you are still there, still turning up, still remembering what happened, and a community with you in it has a continuity that nobody else is supplying.
You are the one who keeps the tradition going
The annual gathering, the standing arrangement, the thing that happens every year because you make sure it does: these hold a circle together long after the original reason has faded. It is real work performed quietly. Notice how much of your group's history exists because you refused to let something lapse. Ask somebody else to take the arrangements for one year, since a tradition that depends on a single person has an expiry date attached to it.
Your friendships do not require maintenance
Long silences are not a problem, obligations are minimal, and picking up after a year takes about ten minutes. That suits you completely and it can leave more anxious people uncertain where they stand. A short message during a quiet stretch costs you nothing and prevents a friendship from quietly assuming it has ended.
A changing circle is felt as a loss
When somebody moves away, a group reorganises or a new person alters the dynamic, you feel it more than the situation warrants, and the instinct is to resist rather than adjust. Nothing about the attachment is misplaced. Notice when you are defending an arrangement rather than the people who are actually in it.
Let one new person in each year
Deliberately, not by accident: somebody added to the circle because you decided to. Left to itself, a group this stable slowly shrinks through attrition and cannot replace anybody. One admission a year, chosen on purpose, is enough to keep the whole thing alive across decades. Choose deliberately rather than waiting for somebody persistent, since the people who persist are not always the ones you would have picked.
Few friends, and they are permanent
Your circle would fit around one table, and most of those seats were filled a very long time ago. Holding a group together for that many years is an achievement rather than a limitation, whatever it looks like from outside. What it also means is that the arrangement has no mechanism for replacing anybody, so a departure removes a structural piece and not merely a name. Adding somebody every few years is maintenance, not disloyalty.
The friendship came first and stayed underneath
Relationships here often begin among people already known, developing slowly out of proximity rather than arriving as a revelation. That produces durable pairings and it means a romance ending threatens a whole social structure. Consider that in advance, since the risk is real and the arrangement is still usually worth it. Where it works, it works unusually well, because the two of you were compatible before either had any reason to perform.
The professional community remembers you
Long membership of a field, a trade body or an alumni group pays out for you specifically, because your value there accrues through years of showing up rather than through any campaign. Keep the memberships current even in periods when they seem pointless, since the return arrives fifteen years later and only for people who stayed.
The future you want is a continuation
What you hope for is largely more of what already works: the same people, the place kept, the arrangement maintained and improved. That is a legitimate ambition and an unfashionable one. State it plainly rather than apologising for it, since a life aimed at continuity requires as much deliberate work as one aimed at change.
Your friends became relatives
After enough decades the distinction stops applying: these people are at the funerals, know the family history, and would take your children. That is an inheritance you constructed. Formalise a piece of it, in whatever way is available, since long assumption is not the same as an arrangement anybody can rely on.