My mom is sleeping with her best friend's husband

Dear Pastor,

I am 20 years old. I wrote you and told you about my husband and his girlfriends but you did not answer me. I know you are busy. Please try and answer this letter. My husband and I have been going together from I was 19 years old.
My mother tried to break us up. She told me she would not accept him as her son-in-law because he is too black. My mother is of light complexion and I am of light complexion. She has two of us. My sister got married to an Indian guy. My mother loved him but he did not treat my sister well so they are now divorced. We are from different fathers.
My mother was having an affair with her best friend's husband and he is not of a light skin. He is black. One day when she mentioned that my boyfriend was too black I told her, "And so is so and so", (I mentioned his name). My mother told me a bad word. I have never heard my mother curse like that in my whole life. She told me to pack my thing and go. I went and sat outside and she pulled down my clothes and was packing them up and I went to the door and said to her, "Mother, I hope you would tell everybody at your church why you are throwing me out".
She continued packing and when my boyfriend came and asked what was the problem she said nothing. When I was taking up some more things she came into the room and said to me, "You are not going anywhere". My boyfriend took me to his parents' house and they accepted me and called my mother and told her where I was. She was crying and she told them to send me back home.
When I got married my mother was at the church long before me. Now she sees my husband as a good son-in-law. I can't say anything bad about him and let her hear. Pastor, I thought that my mother had stopped having sex with her best friend's husband but she is still doing it. Her friend has found out but my mother denied it. How can I get my mother to stop having sex with this man? She says that they are only friends but my sister and I know better. If my mother has a headache he is the first to know and he is there with medication and everything she needs. My husband says I should leave her alone to live her own life.
N.A

Dear N.A.,
I believe your husband is trying to say that there is nothing you could say to your mother that would cause her to change or to end the relationship with her best friend's husband. People may see him visiting her home and some may say that they are having an intimate relationship. Others may say that she is just a good friend of the family. Your sister and yourself know the whole truth.
Your mother cannot be so naive that she would feel that your sister and yourself are ignorant of the fact. This man is a friend but not a social friend. Your husband is right. You should leave her alone.
Now concerning her attitude towards you and your man, for reasons better known to herself, she did not want you to have a man with black skin, so she discouraged you from having a relationship with the man you finally married. She rejected him but you accepted him and finally she has come to love and to respect him. Unfortunately there are so many like her who are prejudice. I know a public figure whose wife described her daughter's boyfriend as a gorilla. He was black and the daughter of light complexion. The young man was educated and had a good career but her parents, especially her mother, rejected him because of his skin colour. Their reaction to that young man caused the girl to suffer depression. I know the case well. The young woman was my counselee. 
Pastor