What does Charlie become after the story ends and why?

At the end of the story, Charlie checks himself into the Warren Home "for good". The things he experienced served to make him more aware of his circumstances, not only in how he envisioned himself, but how he believed others perceived him. He'd remembered enough of what he learned that he knew he no longer wanted to become a source of laughter. He didn't want people to feel sorry for him, and he didn't want to feel sorry for himself. Charlie wanted to take himself away from watching eyes and see if he could find a part of what he'd lost. Knowing what he could have been, and actually achieving all he'd achieved was almost worse than never having experienced it at all. Sometimes ignorance really is bliss.