Family member had a long term affair with OW. Left wife and kids to live with OW overseas. Has caused a lot of pain and anguish for wife and kids. For reasons I won't go into I still need to stay in contact with him but I have made it clear I don't want to become friends with the OW. He has behaved like a complete dick there is no getting away from that, he has done the damage and is going to have to live with the long term damage he has done to the kids. They are very angry with him but he just can't see their point of view and is in full victim mode (wife is evil, no one understands etc)..
But the OW is culpable in this too, she paid to fly to the country he lived in and stay in a hotel with him knowing his wife and kids were waiting at home. He is ultimately responsible for this but as she is a complete stranger to me I have no desire getting to know her given her behaviour. She keeps trying to be nice to me thinking that I'll just charmed into being friends with her and gives no thought whatsoever to the damage they have done.
He is now having a go at me saying I'm judgemental because I don't want to be friends with the OW and why can't I just see what a lovely person she is.