"Do We Have to Go": Same Invitation, Two Completely Different Events

The invitation arrives. Their eyes light up. Your stomach drops. They are already planning the outfit while you are already planning the excuse. Same envelope, two completely different events inside it.
You will go, because you always go. And for two hours you will perform a version of yourself that smiles at strangers, laughs at stories you cannot follow, and watches the clock without looking at it. They will glow, becoming more themselves in a room full of people, while you become less. On the drive home they are buzzing and want to recap, and you are hollow and need thirty minutes of silence to find yourself again. They think you did not have fun. You did. You also spent a currency you do not regenerate easily.
Social energy is not equal, and the gap is the Gregariousness facet of Extraversion. One of you has a deep well, the other has a cup. High Gregariousness treats a crowded room as fuel and leaves fuller than they arrived. Low Gregariousness treats the same room as a slow drain and leaves needing to refill in private. The cup person keeps pouring for the well person, and because the pouring is invisible, nobody notices the cup is dry until it is.
The fix is making the cost visible before the event, not after. The lower-Gregariousness partner can say "I will come for ninety minutes and then I am spent, and that is a real number, not an insult." The higher-Gregariousness partner can plan the recovery in, an early exit or a quiet drive, instead of reading the quiet as sulking. They are not selfish for wanting to go. You are not broken for wanting to leave. You just run on different fuel, and fuel is a fact, not a fight.
You can see the size of each of your social batteries with the 30-facet OCEAN personality test. It takes about 15 minutes, the domain scores are free, and a compatibility report shows whether the party dread is a values clash or only two different tank sizes that were never measured out loud.