I am commenting as someone who had to sacrifice a decade without my children because I understood the dynamics of co parenting. Sadly, the father didn't understand them so he denied me a relationship with them then but when they moved back with me, they were shocked that I insisted that they continue their relationship with their dad and so was he.

I believe that my children wellbeing comes first and if there is a healthy relationship between them, why spoil it? I wonder why everyone can't just part without involving the kids or kid. Anyway, I feel sorry for your friend and his daughter.