Feeling left out in a trio?

The 3 of us are friends, but one of them always acts closer to the other, she doesn't even care about me, I talked to her about this once but she said to me: you are exaggerating. I'm not exaggerating, she literally ignores me, I'm like a bonus extra person there, what should i do, what can i do, i feel sad..
Feeling left out in a trio?
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