The couple, who announced their intention to divorce earlier this week after six years together amid stories of 33-year-old Kutcher's alleged infidelities, had tried to work out their differences but gave up when the fighting became too much, reported People magazine.
"Ashton is unhappy; [Demi]'s unhappy. It just got to a point where they had to end it. The fighting could get pretty intense. Whatever therapy they did was fine for a quick fix but could not get to the heart of the problem," a source said.
Neither party have directly commented on the cheating claims with Moore only releasing an official statement that with "great sadness and a heavy heart" she has decided to call off her marriage to Kutcher.
Kutcher added that he will forever cherish his marriage to Moore.
"I will forever cherish the time I spend with Demi. Marriage is one of the most difficult things in the world and unfortunately sometimes they fail. Love and light, AK," he had tweeted.
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