My mother is cheating on my father, what should I do?

As-Salamu `Alaykum Warahmatullahi Wabarakatuh (May Allah's Peace, Mercy, and Blessings be upon you!)

I am twenty years old. Several months ago, I dreamt that my mother cheats on my father with someone we know via SMS.

I woke up, sought refuge from Satan, and I became confused because I was confident about my mother and never doubted her.

The dream disturbed and possessed me. From another side, I saw that the behavior of my mother changed suddenly where she changed the password of the mobile, I understood that she wanted some privacy which is one of her rights, however the dream and Satan insinuated to me, so I decided to interpret the dream then I cancelled the idea.

I decided to speak frankly with her and told her that I trust her, but I am very annoyed for thinking badly in her even in my dream.

She understood my words and told me that she has no relationship with that person and that she is proud of me, particularly after my frankness with her; thanks to Allah, I felt comfortable and forgot the matter completely.

After a while, I took her mobile to search for something then I saw a message between her and another person that confirms their relationship.

I was shocked and could not find words to describe my sadness. My mother is my model example, how could she do something like that?

My father is a good person, his good situations are countless, and he does not deserve that.

I spoke to her and explained to her my situation of what I saw. She told me that she had an affair with that person a while ago but she cut the relationship completely, and I was relaxed when I heard that, but I still doubt her.

My treating to her has changed, I became cold with her, did not forget her action, and I feel she is a lair and cheating on my father.

I took the number and thought of calling him but my mind prevents me; could you kindly tell me what to do? Should I do it or not?

May Allah reward you the best