Moore and Kutcher ended their marriage last year following allegations that the actor cheated on her with a number of women.
But after pictures surfaced of the "Two And A Half Men" actor kissing new love Kunis, Moore, 49, became hysterical, reported Radar Online.
"Demi is devastated that Ashton has moved on so quickly and is dating Mila. She is beyond heartbroken. Even though Ashton cheated on her all the time, it was with random girls, it wasn't a relationship like it is with Mila and that is what is killing Demi now.
"Seeing photos of him kissing another woman is too much for her to handle, it's like having her nose rubbed in it time and time again. She kind of knew it was definitely over between them but I think she was still holding out a little hope for a reconciliation - now he's actually dating someone else she knows that's not going to happen," a source said.
Kutcher, 34, and 28-year-old Kunis have been friends since working on "That 70s Show" together. The duo are now said to be living together.