Anna Kendrick had made embryos with her toxic ex-boyfriend before their relationship changed.
The 37-year-old actress - who didn't identify her previous partner - described him as "for all intents and purposes, my husband" and explained how he became "a stranger".
Appearing on the 'Armchair Expert' podcast, she told Dax Shepard and Monica Padman: "I was with someone — this was somebody I lived with, for all intents and purposes my husband.
"We had embryos together, this was my person. And then about six years in, about somewhere around there, I remember telling my brother, when things had first kind of gone down, 'I'm living with a stranger. Like, I don't know what's happening.'"
She noted his personality shifted and her partner later told her he had feelings for another woman, but she tried to work on the relationship despite the issues.
She added: "It wasn't just the, 'Oh, I'm losing a relationship.'
"It was that I believed that if we broke up or, you know, if he left basically, it was a confirmation that it's because I'm impossible, I'm lucky that he's even tolerating my bulls***.
"There was an inherent thing of me being so rejectable that this person who loved me very deeply for six years, it suddenly occurred to him, how awful I was or something. The shame, that lingers much longer."
To deal with the relationship, the 'Pitch Perfect' star "dismantled" her life, telling her agent she needed "time off", and going to AI-Anon, an organisation to help friends and family members of alcoholics.
She explained: "I did start going to Al-Anon while all this was going on. I mean, look, I truly dismantled my life, and at first, that was as a reaction to the accusation that I was crazy and I was the one causing the problem.
"So I had a conversation with CAA, my agency and said I need to take time off, I have a mental health problem...
"I started seeing two therapists a week and I started trying to learn to meditate and I got into Al-Anon and all of these things ended up being very wonderful things for me in the long run, but initially went into them thinking, 'Tell me how to stop being crazy. Tell me how to stop feeling anything.' "