I read it 25-30 years ago. Maybe called something like 'Baby Club'
Three couples with young children, each with various issues. They all hang out together.
One of the guys ends up having affairs with the other two women. He is kind of overwhelmed by it - I think the women initiate the affairs.
His wife leaves and he struggles to cope with the kids and I think the other couples step in to help?
And it ends on a Greek Island? His wife goes there to write - maybe?!
Any ideas?....