If one becomes irredeemable after having an affair, then at least 95% of the people who post to these boards should instead simply file for a quickie divorce.
And, FWIW, I'm not trying to push your buttons. I just think it is very sad for your children to have what functions as part of their extended family (their father, his GF, the other children) in most ways rejected by their grandparents.
As for friendship, I certainly don't think there is reason for you to be friends with either one of them. I certainly wouldn't be if I were you. Yuck.
