Who is Barbara from Arnold: The Education of a Bodybuilder and what is their importance?

In 1969, Arnold met a young woman named Barbara, who was working as a waitress in Santa Monica. When he asks her out, he finds she is completely different from all the other girls he has known. She knows nothing about bodybuilding and genuinely cares for Arnold as a human being. When she returns to school at the end of the summer, Arnold leaves for Europe, but he continues to write to her and talks about her to all his friends. When he returns from Europe, they decide to live together in Santa Monica. Unfortunately, Barbara realizes that Arnold won't slow down, even though he's at the top of his sport. He has just embarked on a career in movies, and thus, she concludes they can't stay together. While Arnold is in Alabama making "Stay Hungry," Barbara moves into her own apartment. He is devastated by their break up and realizes, too late, that he doesn't know how to appreciate women properly, nor does he understand the meaning and significance of a sincere and honest relationship.