Sarala Chaudhary or Sarala Devi was the daughter of the elder sister of Rabindranath Tagore. A highly educated woman for her times and was very beautiful.
Gandhi had written about his relationship with Sarala Devi in a letter to his friend Hermann Kallenbach “Our relation is beyond definition. I call Sarala Devi my spiritual wife. One friend has described it as a wedding based on knowledge.”
There was nothing sexual in the relationship between Gandhiji and Sarala Devi. And you have to look at one angle also that is Gandhi had the moral courage to tell the truth even about his feelings for the beautiful Sarala Devi because there was no ethical corruption in his mind. There was nothing 'confidential' in his life as he practiced what he preached.