Obi's identity is shaped by two dual forces: Western culture and values and Igbo culture and values. Though Obi embraces Western values as evidenced through his education and his nominal adherence to Christianity, we can see how this decision alienates him from his traditional Igbo culture. For Obi to identify with Western culture means that he rejects a number of cultural traditions including polygamy, paying a bride-price (misunderstood by the British as "buying a wife"), honoring a man because of his many "titles" earned through competitions, religious observance, etc. Embracing Western culture means embracing the many positive and negative things that came with the industrial revolution and other defining moments of Western history.
Obi sees himself as a pioneer. He wants to change the corrupt system of bribery and nepotism, and he wants to marry a girl that traditionally is taboo. We can see how much this identity meant to him when he cries after the judge asks how a man of such "education" and "promise" could have accepted bribes. He has failed. And now that too is part of his identity.
Although Obi sees himself as an individual, his kinsmen maintain a group identity and incorporate Obi into their system of socialism and nepotism, creating a web of obligations and expectations that Obi finds difficult to escape.
Obi identifies himself as an educated Igbo, believing that he is as fully Igbo as he is educated; but in reality, his education has isolated and alienated him from his indigenous culture.