Thank you so much for your help both @Nanren888- 新西兰 and @Jazz!

Hello Noonoi. When he says, "we are infinite" he means that he and his friends are very much alive. He feels that they have endless power. It is about feeling young and unstoppable. At that moment, he feels like everything is attainable. It is a very positive and invigorating feeling to have. He is happy and feels very confident about life.

http://gingersass.com/tag/the-perks-of-being-a-wallflower/ Or, I guess I did some re-reading. The Perks of Being a Wallflower is such an amazing, poignant book. There’s one moment in the book that makes me feel alive every time I read it. As my one friend said, that page is like “anything is possible and every bit of the world is not only alive, but within reach.” The main character, Charlie, is having an absolutely perfect moment with his two friends, Charlie and Sam. He narrates, “And in that moment, I swear we were infinite.” . It seems to simply be a total misuse of the word "infinite: as so many words are misused to good effect so often. The authour of this page suggests that the meaning is one of “anything is possible and every bit of the world is not only alive, but within reach. infinitely capable,