actually we just had a friend of ours wife left him and took his 4 kids...She was NUTS always making up lies so we would take her side, now we know better
I did not pick anything because it would depend on the situation and half the time, you never really know the whole story. I guess I would stay out of it completely.
You stay friends with the one you were friends with if the relationship happened before their marriage. She/he is going to need an unbiased, but honest friend during a time like this. You can't straddle the fence. That causes more pain and hurt!
Then again if you don't want to lose either friendship, StAY OUt of it!