Some things are just unforgivable.
For Demi Moore, husband Ashton Kutcher's one-night stand with Sara Leal on their sixth wedding anniversary turned out to be a hurt that she couldn't overcome -- leading to her painful decision (announced Thursday) to call it quits on their marriage of six years.
"The final straw with Sara Leal has just been too humiliating for Demi to get over," a source close to the former couple tells Us Weekly. The Two and a Half Men star, 33, had sex with San Diego party girl Leal, 22, in the wee hours of Sept. 24 in his hotel suite. As Leal explained to Us, Kutcher claimed at the time that he and Moore, 49, were already separated.
Margin Call actress Moore "just couldn't look at Ashton the same way and the marriage... completely unraveled," the pal explains. "She still loves Ashton but feels he went too far and disrespected her and their marriage in a way that can't be taken back."
Three other factors? Rumer, 23, Scout, 20, and Tallulah, 17, her daughters with second husband Bruce Willis. "She wants to set an example for her daughters and this was just something she could not rationalize to them or to herself."
And, indeed, she tried with months of counseling and heart-to-hearts with friends. "She really tried everything she could to forgive him and accept his apologies," the pal says. "At the end of the day, the public humiliation and the example she was setting by staying in the marriage just wasn't the right thing for her."