Confused

The character that is Billy Bibbit is an enigma. At first he seemed like he was a submissive and weak man who liked to be left alone and didn't like to be the center of attention. His constant stutter made him look like an insecure manchild who never had many friends and has always been overprotected by his mother his whole life. But toward the end of the book, all of this changed, or maybe it was left in the back of his mind. 

He began to speak up more often and share his thoughts, even after being practically destroyed by Nurse Ratched in the group therapy. He is often found around the other patients, especially McMurphy and Harding, and they become good friends. That is when Billy starts to quickly change to fit in with the more outgoing patients. He agrees to going on the fishing trip, something he would have seriously doubted before, and using his natural boyish charm he picks up one of the prostitutes and invites her to the ward another day. But the real shocking decision he made, driven by his original personality, was to commit suicide due to the pressure Nurse Ratched put on him by threatening to tell his mother about his night with Candy. He clearly couldn't handle the thought of his mother knowing he was with a woman; this shows he certainly has some maternal issues. He let McMurphy and the others carry him away and make him take bad decisions, and he couldn't deal with the consequences. This was the big change Billy went through throughout the book: he assumed great power, but didn't take great responsibility.