Third Friend
A Third Friend is someone who is not in the primary circle. They are not the first or second choice, but a situational choice.
What does it feel like?
It is to sit across your "friend" and listen to them talk on the phone and tell others their plans for the week, when all you had got was "nothing much" when you had asked them the same thing.
Have an issue that cannot be solved by your immediate friend group? Go to the third friend.
The third friend is someone who is "close" only in a narrow sense. When you are a Third Friend to someone, you might be close to them in how much you know about them, but as a constant, you are not part of the joys and fun part of life. You are relegated to the labour parts of the friendship (if you could call it that).
But in essence, it is not a friendship. It's a friendship disguised as a person using another to do the labour parts of a friendship that they don't want first and second friends to bear.
It is to bear your friend in struggle and emotional turmoil, yet not holding them in joy, not because you can't, but because they didn't even tell you.
Being a Third Friend is to know the struggles of your friend but not being invited when they plan a hangout. It is to know all the emotional weight your friend is carrying but never holding them in their joy. When they share a joy, you are not on the list.
It is being called only when chores require being done or when they "need an ear." You aren't part of their life. You only see the ugly parts, so they can show the good ones to the friends they actually care about.
Many times it's transactional. They will listen to your problems, offer support and help, but you get to see it after a while: they have not really thought of you as a person. They offer support without understanding you.
They do it because they feel obligated to. To return the "favour" of the support you give them.