How and why does Gandhi end his relationship with his wife in the biography, Gandhi?

Despite his interest in women's rights and his claim of great love for his wife Kasturbai, Gandhi ends their life together as husband and wife by taking a vow of lifelong celibacy. In many ways, Kasturbai plays the role of a traditional Hindu wife, staying in the background of her husband's life and submitting to his authority, even going to prison for his cause and reluctantly accepting an "untouchable" child into their communal village.