My parents are both in their 60s and have been divorced 6 years. I don't know whether or not my dad was faithful while they were married, but it honestly wouldn't bother me at all one way or the other because my Mom was a pretty wretched human being, so I wouldn't really blame him for seeking some kind of affection from another woman. However, I just found out he apparently has been "the other man" the past 6 months in an affair with an old high school girlfriend. The husband mailed a letter to my mom's house (our family address), opened the letter and passed it on to me. It was short and to the point and basically just said the above, that my dad had ended their marriage, and that this guy didn't even care because of what a piece of crap his wife is.
I'm confused as to how I'm supposed to feel about this. My family is a disaster in numerous ways, so I separated myself physically and emotionally from them a long time ago. Obviously being the other man or woman is not morally correct, but I feel pretty indifferent about the whole thing. My dad is a good man overall and was a great father. I'm an adult now, so I understand he's human and just a person like you or I. I wonder if perhaps I'm not reacting appropriately though? What would be your reaction if this happened?