After a six-year union that had endured insecurities, emotional strife, and cheating scandals, Demi Moore and Ashton Kutcher finally call their marriage off after a last bid to salvage it fails. This week’s issue of PEOPLE examines the final days of their bitter split and the emotional battles that turned their relationship toxic.

When Demi & Ashton touched down on the ultraprivate Caribbean island of Parrot Cay on Nov. 11 just in time for Demi’s 49th birthday, their mood couldn’t have been darker. “She looked drained,” says an observer who saw her before her flight. And the stakes were never higher. “This trip was about their relationship, figuring out what to do,” says a friend. “They gave it one last try.” For two days the couple hashed things out in their subtropical paradise: Where could they even go from here? After everything – the public humiliation of his two tabloid cheating scandals; her increasingly gaunt appearance amid friends’ concerns for her well-being, the fights, the counseling – could this union be saved?

When they arrived back home in Beverly Hills, Kutcher, 33, somberly began phoning friends with the answer most of them had seen coming for months. Then, on Nov. 17, Moore let the world know in a sharply worded, pointedly solo statement that pulled the plug on a marriage that had seemed to be on life support throughout the past year. The truth is both Moore and Kutcher were beyond exasperated with a union that had turned toxic.

“Ashton is unhappy and she is unhappy,” a Kutcher sources tells PEOPLE. “It just got to a point where they had to end it.” Adds another source: “They were fed up with each other.” In the end, say friends, the issues that had long fueled skepticism about their unlikely romance – the 15-year age difference, his wandering eye, her insecurities – ultimately proved their undoing. “The marriage has been deteriorating for a long time,” says a friend of the Two and a Half Men star. “Ashton was ready to end it, [but] he wanted to wait for Demi to actually do it. He loved her but couldn’t live with her.”

For the past year the same passion that had once launched a thousand public displays of affection was now fueling increasingly hostile rows. “The fighting could get pretty intense,” says a friend. Although the pair engaged in rigorous counseling based on Kabbalah, the mystical Judaic teachings that became their shared spiritual foundation, it wasn’t enough. “Whatever counseling they did was fine for a quick fix,” says the friend, “but couldn’t get at the heart of the matter.”

Long open about his affections for his stepdaughters (Moore’s daughters with ex-husband Bruce WillisRumer, 23, Scout, 20, and Tallulah, 17), in private Kutcher also expressed his yearning to have children of his own with Moore. Although the couple dismissed any obstacles posed by their famous age gap – last year Kutcher praised his wife as a “genetic freak,” insisting that he was “not worried” about infertility issues – reality eventually seeped in, creating some of the first fissures in their relationship. After the initial cheating scandal in September of last year, Kutcher told a close acquaintance about his frustrations. “He knows that with Demi he won’t have kids,” the source said then. “When he married Demi, he didn’t realize it at the time. He didn’t get it.”

With the couple’s estimated combined net worth at $290 million, friends say they don’t anticipate a contentious divorce. “Demi is moving full force ahead in terms of work,” says a source of Moore, who lately has been stepping into the role of producer on several projects. Adds a source close to Kutcher: “When two passionate people like Ashton and Demi end their run, the best thing to do is to move ahead on their own. After the initial pain wears off, they’ll have had time to reflect. They both have a great deal to offer. And plenty of time to find happiness.”

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