Unfaithful

This isnt about me , its about my mother . As im not married , im a single parent. My parents have been married for 25 years . Shes very young still shes on her early 40s . Ive discovered that she talks to other men , she chats with them and im mostly certain she meets with them .  Shamelessly she does this infront of my father . My father does not deserve this !. And this is not just coming from me , anybody that knows my dad knows he deserves better and that he is a respected men. I cant find what to do , as you know i dont have the best communication with my mother. I talked to my grandmother about this and she was shocked!.. She spoke with her and all she sais is that its her life . What should i do ! Help . I cant support this! I cant let it continue even if my father doesnt do anything about it , i know hes hurting him and its not fair, its not right!. Help , advice please