What does "i can't be who you are " mean?

my best friend I met my best friend at college. We were roommates and had a very good time the first two years in college. The third year she went to America for studying. But we still kept in touch on-line, sometimes we called each other. After two years' study and one year's work she came back to China. The day I knew she would come back is one of the best days i've ever had. Now we live in two cities but near to each other. The reason we can be the best friends is we make both of us better persons. She will be my best friend forever.