The Hollywood actors ended their relationship last December (09) after 23 years together and Sarandon was stunned by the public reaction to the break-up.
She tells Britain's Stella magazine, "People were coming up to me in the street and saying, 'I cried and I cried when I heard.' Well, I was sadder. I didn't think it would ever happen either. "
And Sarandon, who was previously married to Chris Sarandon for 12 years, admits she thought keeping her union with Robbins unofficial would give the relationship longevity.
She adds, "I thought that if you didn't get married you wouldn't take each other for granted as easily. I don't know if after twenty something years that was still true. You bring people into your life at certain times. Maybe you have a relationship to have children and you realise that it's fulfilled after that point."