The best friend groups have a door, not a wall. Watch how yours treats the new person.

Groups show their character in the first ten minutes with somebody who does not know the jokes yet. A closed group is not usually cruel; it just keeps talking in shorthand and lets the new person stand slightly outside it. That is a choice, even when nobody decides it out loud.

At the next thing you go to, find the person who knows the fewest people and give them something to do with you. Explain the reference instead of laughing past it. Watch what your group does too, and say something if it keeps closing.