You are what holds the group together
Put a Libra Sun in the house of Community and you become the connective tissue: the person who knows how everybody feels about everybody, who smooths the introductions and who notices when a group is about to split. You need collectives where that work is valued rather than assumed.
It is a genuine social architecture and it is almost entirely invisible. Groups that lose you discover within a year how much of their cohesion was one person doing unpaid maintenance.
How the group is run matters to you
Process, representation and whether decisions are made openly affect your commitment more than the cause does. A worthy organisation run unfairly will lose you; a modest one run well will keep you for twenty years. That is a coherent principle and worth stating out loud, since people otherwise read your departure as a loss of interest.
Factions are where you get caught
When a group divides, both sides assume you are with them because you have been reasonable with both, and you end up carrying information across a line you never chose. Say early and publicly what you will and will not do. Neutrality announced in advance is a position; neutrality discovered in the middle looks like duplicity to everybody.
Causes about fairness rather than about intensity
What moves you is inequity rather than emergency: the rule applied unevenly, the group excluded, the arrangement that quietly favours some people. That is a durable motivation and it produces slow patient work rather than dramatic gestures. Choose organisations doing that kind of work, and resist being recruited by whichever cause happens to be loudest this year.
Belonging without holding it together
The version of this to aim for is membership without responsibility for everybody's comfort. That means joining a group where somebody else does the cohesion work. It will feel oddly passive at first and it is the only way you get to find out what you actually enjoy about a collective, rather than what you enjoy about being necessary to it.
The person who knows how everyone feels
You hold an accurate map of the relationships in every group you belong to, including the tensions nobody has named. That makes you valuable and it makes you a repository for other people's grievances. Decline the role of confidant on one or two of them, kindly, and notice how much lighter the group becomes to attend.
A network held together by you
Professionally your value includes a wide set of people who trust you and who mostly do not know each other. Introductions are your highest-leverage act. Make one deliberate connection a month between people who should meet, and keep a note of what came of it, because that record is your actual professional asset.
Everybody has an opinion about your relationship
A partnership formed inside your circle comes with a permanent audience, and you will find yourself managing their reactions as much as the relationship itself. That management is invisible work and it is entirely yours. Decide with your partner what the group does not get told, and hold the line even when a friend is hurt at being outside it, since the alternative is a relationship conducted by committee.
Everything split evenly, by you
Group costs, shared trips and collective purchases end up administered by you because you care that it is fair. Use a system rather than your goodwill: a shared record, agreed in advance, that does the arithmetic in public. It protects the friendships and it stops you quietly absorbing the rounding, which over a decade of holidays and dinners is a considerable amount of money.
Being a member rather than the glue
Somewhere there is a group you could belong to without being responsible for it, and finding one is worth more to you than another organisation to run. Look for the room where you are the least connected person present, and stay long enough to find out what it feels like to simply be there.