DEVASTATED Angelina Jolie kept a poignant diary that reveals the secret reason she walked out on her husband Billy Bob Thornton and rejected her famous father, actor Jon Voight.

Jolie, 27, was changed after harrowing and heartbreaking journeys to impoverished Africa and Cambodia left her unable to relate to Billy Bob or her dad, say sources.

"Hollywood seemed like such a shallow and trivial place to be after the pain and suffering she witnessed," says a close family friend.

"She felt that no one - not Billy Bob, not her father, not her close friends - could understand the many horrors she experienced during those trips."

Pals say she'd try to speak to Billy Bob about the suffering victims of land-mine accidents or the homeless children she saw. He was sympathetic, but he couldn't feel what she felt.

"Finally, Angelina chose to simply shut down," says a source.

Just before her first trip to Africa in February 2001, the actress wrote: "I love my husband very much. Billy Bob didn't want me to go, because he loves me. But he is supporting my need to go," according to a source who viewed Angelina's journal.

She added: "My dad attempted to cancel my trip. He called USA for UNHCR (United Nations High Commissioner for Refugees), the organization sponsoring me, but he couldn't stop me. I was angry with him, but I know he loves me and felt a need to protect me."

Sources say Billy Bob and Angelina's dad feared for her safety overseas.

"Neither Billy Bob nor Jon could understand why Angelina couldn't just work for the cause from her home in Hollywood," says another insider. According to sources, it was her trip to Cambodia in July 2001 that changed Angelina forever.

Her diary includes heartbreaking descriptions of the victims of land mines she met and photos of tortured prisoners she was shown.

"I can't breathe ...," the source says Jolie wrote while in Cambodia. "I saw photos of mothers being killed as they held their babies in their laps."

When she returned home to L.A., she was plagued by guilt.

"Angelina says she felt terrible for sleeping in a clean bed and eating a healthy meal," says the source. "She kept seeing the faces of starving men and women ... of children whose hair was falling out from malnutrition."

It wasn't long before Billy Bob was feeling neglected and telling Angelina that he wanted his wife back and wanted to have fun together again, says a source.

The pair, who carried vials of each other's blood around their necks, were one of Hollywood's most eccentric couples. Billy Bob admitted he liked to wear Angelina's pink panties when they were apart. And they loved to dress up - she was Little Red Riding Hood and he was the Big Bad Wolf.

Billy Bob missed all that, say pals.

"He asked her to put all her horrible experiences behind her," says another source. "But Angelina told him that after all she'd seen, she couldn't pretend she had never experienced it."

She felt she had to do more to help.

"That is why, in November 2001, she convinced Billy Bob to travel with her to Cambodia, where they began adoption proceedings for baby Maddox," says the source.

But the addition of Maddox wasn't enough to keep the marriage together. And in July 2002, she filed for divorce from Billy Bob, 47.

Angelina's dad Jon alienated her even further when he publicly stated, soon after the divorce filing, that she had serious mental problems.

"In the end, Angelina felt so alone that she broke from both Billy Bob and her father," says the source.

"Now Angelina's life revolves around her son, Maddox.

"She will never let him forget the country he came from, and she has promised to do anything she can to help the people there who still struggle to live."