The "Ghost" star was married to Kutcher from 2005 to 2013, during which she underwent in vitro fertilisation treatment.
The former couple eventually conceived a daughter, but Moore miscarried at six months, and when she struggled to fall pregnant again, she suffered a relapse in her longtime battle with substance abuse.
Rumer Willis admits it was one thing watching her mother develop an obsession with Kutcher, but when Moore became fixated over starting a family with the "Punk'd" star, it made her and her two younger sisters feel less than adequate.
"So much of that time, especially with Ashton, I was so angry because I felt like something that was mine had been taken away," Rumer, now 31, shared during a candid conversation on Jada Pinkett Smith's "Red Table Talk" series.
"I think also, when she wanted to have another baby and then it wasn't happening, and there was so much focus on that, it was like, 'Oh, well we're not enough.' "
Rumer confesses it even drove her out of the family home: "Part of the reason I moved out of the house was, I think after you had a miscarriage, I literally was just like, 'Why are you so desperate to have another kid?' I couldn't stand the idea," the 31-year-old admitted.
And it was just as hard on Tallulah Willis, Moore's youngest daughter with her ex-husband Bruce Willis, as she soon became the only one still living in the house with Moore and Kutcher.
"Watching the behaviour with Ashton, those years, because everyone had left the house and it was just me living there, I felt very forgotten and I feel like I developed and nurtured a narrative where she didn't love me and I truly believed it," Tallulah, now 25, said of her then-fractured relationship with her mother. "I know that she does, 100 per cent, but in that moment, you're hurt."
And Moore, who is now sober again, acknowledges the tough time her children went through as her addictions really took a hold of her life - leading to a three-year estrangement.
"The addiction and the co-dependency... like my addiction to Ashton - that was probably almost more devastating because it took me seriously away emotionally," she shared.
Moore is also mum to 28-year-old Scout Willis, who was unable to join her mother and sisters for the "Red Table Talk" chat.