Australian beauty Nicole Kidman insists mental unfaithfulness is far more damaging than adultery when it comes to failed marriages. The Moulin Rouge! beauty is now happily married to country star Keith Urban, but was divorced from ex-husband Tom Cruise in 2001 after nearly 11 years of marriage. She says, "I don't think that sexual faithfulness is the most important one. It is the easiest type to define, but mental unfaithfulness is far more subtle and dangerous. "How far can you go in this type without being really unfaithful? It's a difficult issue..."