Why is it easier to forgive family for indiscretions like infidelity and lying?

The title pretty much sums it up - I have been witness to my own family and with the families of others that when someone is responsible for cheating on a spouse or SO that the family is the first one to come to the aid of the one doing the cheating or lying. I have always taken issue with this. My brother-in-law is an example - he cheated on his wife of 5 years right before Thanksgiving of last year - he then brought the mistress to the family Christmas party. His mother and Step Dad fully accepted her and actyed as if nothing had happened. My wife and I basically were cordial to the woman but slightly scornful to the BIL. I couldn’t understand his silly rationale that what he was doing was just OK. So here is a hypothetical scenerio:

If your 35 year old son cheats on his wife of 10 years and leaves her to live with the mistress do you stop talking to your son because you don’t agree with his actions?
Do you scold him and move on - getting to know the new woman, and not speaking to the former wife?
Do you empathize with the former wife, and then still get to know the other woman as well as you knew the first wife?

What would you do?

My father is a good example of this. He just divorced wife #3 and cheated on all of them including my mother. The list of other indiscretions is too long to list. Just think of anything other than murder or rape and he has done it. He was never a real father to me either. My stepfather was much more of one. He calls about every 6 months and never gets anyone, including my young baby daughters, any presents. He has only seen my oldest twice and my youngest once. He always claims that he is coming to visit and never does. The only time I got truly furious and disgusted in recent memory is when he got fall-down drunk at my first daughter’s christening.

He called a couple of days ago and ended the 3 minute conversation with “You can’t imagine how much I love you and the girls”. My reply: “I love you too daddy”. I can’t explain why other than the fact I know he meant it in his own way and he will never change. Blood is thicker than water in my mind. If it was any type of non-blood related relative, I would have rejected him a long time ago and have done it to other non-blood related relatives for much fewer reasons.

I think that the answer is that “goodness” in a person is not black and white. People can make mistakes, can hurt others without thinking about the consequences, and do all sorts of selfish things, and yet still be loving and caring people who are deserving of care and love.

I have a relative in my extended family who’s had a hard time with fidelity. He’s caused quite a bit of pain to his second (now ex) wife (don’t know the history of him and his first wife), but I don’t think he’s a bad guy. He’s bright, funny, and cares for his family a great deal, but, to psychoanalyze a bit, has a really hard time with age and growing old, and I think that his marital issues revolve around a deep and subconscious fear about being an “old man.”

I’m still close with his ex wife (who really is a part of the family after, oh, probably 20 years or so), and I’m still close to him. She was done wrong by, but I can’t hold a permanent grudge or anything like that.

I don’t at all condone his actions, but I understand that he is truly trying to find happiness and contentment in this world. Not everyone goes about it in the same way, but I can generally see a bit of myself in that journey, in whatever form it takes, and so can empathize and learn from it.

Using your scenario, I’d probably have some pretty strong “I raised you better than that” words for my son, and he’d be obligated to at least endure them. After that, I’m not sure what kind of relationships would shake out. Certainly, I wouldn’t stop loving my son – can’t help that. But respect and other aspects of our relationship may take a hit, depending on the why-for and where-as of it all.

Why is it easier to forgive family? I suspect that actor-observer bias (“If others do it, it’s their fault; if I do it, it’s not my fault, it’s because of the situation I’m in”) may be involved, with “if I do it, it’s not my fault” extended to “if my son/daughter/brother/etc. does it.”

IMO your example is also in the eye of the beholder - If I had observed it in your place I’d probably seen it in terms of “A and his wife B separated, divorce probably in the works, now A is seen with new partner C”. I wouldn’t expect from someone whose marriage has failed to stay celibate until the divorce is through, family or not. The “cheating” part would be a matter of timing to which I hopefully would not be privy to.