Charlie thinks that Sami (Emma Watson) and Patrick (Ezra Miller) are dating, and rather likes watching things from the outside, like a kibitzer at a chess tournament. Charlie says he wants to become a writer, but he needs people to write about. He still needs to keep his distance. But, at a low-key “initiation” party, Charlie walks in on Patrick having a gay encounter with a make classmate. Patrick asks him to keep a secret. But the incident will draw Patrick into his own real life.
In the film's "middle section", Charlie grows enough to act in a musical -- specifically, "The Rocky Picture Horror Show", where the "penalty" is to go into drag. It's rather tame and non-threatening, fortunately. (I saw the stage version in Minneapolis myself in 2002.)
I saw the film Saturday afternoon at the new Angelika Mosaic in Merrifield, VA, in the largest auditorium, curved screen, prefitted to regular aspect. There was a small crowd.
And why does the movie title say "being" rather than "becoming"?