The 'Lovelace' actress is good friends with the action movie icon, and feels he cannot be solely held responsible after he had an affair - and fathered love child Joseph, 15 - with their housekeeper Mildred Baena while still with his ex-wife Maria Shriver.
She said: ''Whatever happened in their [Arnold and Maria's] home was happening with both of them. It's a terrible thing - and it's easy to say 'Oh, it's just something that he did', but this took place in their home, over a decade. It happened with both of them.''
Despite this, Sharon did reveal she was ''disappointed'' with the revelation of the 'Last Stand' star's affair.
Talking to the Sunday Times newspaper's Style magazine, She continued: ''I have a very frank relationship with Arnold. Was I disappointed? Who wasn't? Nobody is excited when people betray themselves and their families. No one goes, 'Yay, good for you.' ''
Despite their failed romance, Arnold recently spoke of the ''wonderful relationship'' he has with Maria as they work together to raise their family despite their separation.
He said: ''Under the circumstances, living in divorce, I have a wonderful relationship with my wife. There are no fights, we talk all the time on the phone and we raise the kids together.
''We are responsible parents and we know the only way it works is if both of us work together and that is working really well.''