Jo - I agree with you completely. Sorry but OW and her D are not family. Even though you and Andy aren't married, you are still family. I don't think I could go either in your sitch.
As for being friends, I feel the same way about my XH. To be friends with him without loving him doesn't work for me. There will always be a part of me that will want more. I hope to keep him in my life that I can still be a part of D9's life, but I know a real friendship can never happen between me and XH. I've never been able to figure out how to unlove someone.