In the new issue of People magazine, Moore's inner circle says she is "jealous and frustrated," and "she's not in a good frame of mind."
"Breakups are hard in general, and it's hard to see that somebody that you loved and you shared a life with has moved on so easy, when you haven't," New York relationship expert Siggy Flicker said. "It's a little bit of a crush to the ego, but she [Moore] can survive this."
Kunis, who starred with Kutcher on "That 70s Show" for eight seasons, is not only 20 years younger than Moore, but she was recently named the sexiest woman alive by Esquire magazine.
Kutcher, 34, and Moore separated in November after six years of marriage. Less than a year later, Kutcher and Kunis, 29, have been photographed many times holding hands and kissing.
Kutcher's split with Moore came on the heels of his alleged infidelity. Still, some are surprised how quickly the "Two and a Half Men" star has moved on.
"The moment that he and Demi announced their split, he was sort of having this wild party-boy stage," People magazine reporter Carlos Greer said. "But he kind of toned that down quickly and he and Mila seem to be very serious."
Moore, who turns 50 next month, has been candid about her past struggles, including, among other things, her body image. Moore's friends say things hit rock bottom in January when a 911 call was made after she was found barely conscious.
The actress had reportedly smoked synthetic marijuana and had to be hospitalized. Moore later entered rehab for substance abuse issues. Close friends of the "G.I. Jane" star tell People "she was struggling, and she was sad."
"Demi has dealt with the split differently from Ashton," Greer said. "He's been very public. She's kept a low key profile. She's been relying on her extremely close friends and her Kabbalah faith."
Kutcher was Moore's third husband. She married musician Freddy Moore in 1980. Moore later married actor Bruce Willis in 1987 and had three daughters.