This is serious - I need mature advice about my cheating husband?

He is not only after sex. They are having a common affair with both sex and emotional connection. You're his nagging wife. She's his loving mistress. You belittle him. She admires him for being that special father or for whatever else. The more you confront him the worse you will look to him. Especially when compared to her. She does not have to be mean to your husband because she has her own husband to fight with. Before you confront him decide what is that you're trying to accomplish. Are you trying to break them up? Even if you succeed he will not be nicer to you after that. He will hate you for breaking his fairytale relationship. And he will soon find somebody else to fill his need for being loved. You either accept things as they are or leave. Either way no point to confront him. Just my two cents.