This is one I struggle with too. If my H and I were friends how come he brought OW1 into my house and screwed her when I was visiting my dear friend who'd just been diagnosed with cancer? I doubt there's a "friend" in the world who'd do that. Yet he insists we should try it. He says it makes life easier. For whom?
Intellectually as a concept it seems like it's a cool thing to do. In reality, some days I manage it, some days I don't. Mostly I am civil. Friends, no, not really. My friends would not open me up and eviscerate me like he did. However we have no kids. Maybe that changes things. Yet, we work together, so see each most weekdays.
So in a very convoluted way I am saying, who knows if its doable! X