My mom will be hurt if I tell her – Young woman seeks advice after she found out her father has a married side chick

“I need your advice please. My dad is working away from home. He rented an apartment and comes home during the weekends. The rest of the family, we live in the village,” she wrote. 

After I finished my secondary school, my dada gave me his smartphone since he had another. I came to discover that he has a side chick and the worst thing is that they often have sex and he spends too much money on her and her three children. Even my own mother and we as siblings he has never spent such amount of money. 

This woman is also married and they are not separated with her husband. My mother visits my dad at times and knows this woman as a neighbour and they are good friends since she also rented there. Her room and my dad’s room are opposite. 

My father has her photos and videos in his phone. I have this woman’s number in my phone , her photos and those of her children, their videos and I also have screenshots of their conversations and money transaction in which my dada sends to her. 

I don’t know what to do as what i want is to stop this relationship at once.we are suffering in the village in the name that he has no money. He got married to my mother in the church although my mother was a Muslim she transformed to a Christian due to the love she had to my father. 

My mom has been loyal to him all these years. She has been open to me as her first daughter when a man approaches her she refuses and if any man demands her number she usually gives him my dad’s number. 

I have not told her about the affair my father is having with this woman because I know she will be hurt and it could lead to her health deteriorating since she is asthmatic. What do i do to save this marriage and mostly my mother as she is everything to us. Kindly i need your advice am confused Please.