A hermit is a person who decides to live a life of solitude mostly for religious purposes. The reason for deciding to live a life of solitude far from people and the place he is accustomed to is to look for a solution or to find out about something. However, it doesn't mean the person won't talk to people he meets. He will but his main purpose is to find the 'truth' about something.
In the book, a black hermit refers to an African hermit due to the fact black colour is associated with black people - Africans.
Remi ran away from his people in the countryside and got lost to the life in the city. The reason for running away is because he was escaping from a wound in his heart which is Thoni. Remi believed that Thoni knew he loved her but decided to get married to his elder brother. He hated his mother because together with his late father, they forced him to inherit his brother's wife according to the customs of the Marua tribe.
He ran to the city to find the meaning of his life. But, did he? No. It's until the elders and the pastor visited him that he learned what was required of his life - what he was supposed to do or what he was created for. He learned what was required of his existence.
When Remi revealed to Jane that he wants to go back to his village and he is married, she told him that he doesn't know what he wants in his life while she knows what she wants in life - who she wants to become or the direction of her life. She told him that a hermit is a person who seeks the truth.
Before revealing to Jane he's married, he told himself he has been a hermit for too long. What the elders and the pastor had discussed with him made him realize his purpose in life.
Remi goes back to his people because he knows he is the one who is supposed to steer his tribe in the political direction and as a politician and a leader, he knows things that need to be adjusted/changed in his tribe because of his education.