Salam aleikum, I recently sent a question to you but forgot to add a very important detail. I will repost the question and add it in the end, sorry for the inconvenience.
Let’s say a woman who is shia muslim and lives in a western country, went to a western court and filed for a divorce from her shia muslim husband due to years of marital issues. The non-shar’i’ divorce was granted to her, afterwards she moved out of the house and moved in with a strange christian man instead while living separately from her husband. The eldest son knows about this situation, and the mother tells him that she had sex with the strange christian man. After some time the mother kicked the strange christian man out of the house and repented to Allah for what happened. What should the eldest son do about this situation and must he tell his father about what his mother did?