The couple became engaged in March, 2018 but by the end of the year, the "Survivor" singer was convinced he wasn't her life partner and called off the marriage in December.
And now she admits the decision weighed heavily on her and took her down a dark road.
"I was weak, very depressed and thinking it was the end of my life," she tells Essence magazine. "If someone had asked me where I would be today, I didn't think I would be alive, because I was so broken."
"It felt as though I had failed publicly and privately, too, and that was just not like me. I was like, 'God, there's got to be more'."
Michelle admits depression grabbed her when she started planning her wedding, and she sought help in rehab.
"I'd been there before in that darkness and I was like, 'No, you better go'," she explains. "By the time I got there (rehab), I was stable. However, I would've understood if he left. He's been praying for a wife. He didn't pray for a depressed wife."
Williams then suffered a nervous breakdown, which forced her to pull out of the Broadway production of "Once on This Island", but the singer tells the magazine she is in a much better place now: "I am not perfect. I'm not preaching. I'm just telling you what I'm doing right now - I'm sticking to my routine. When people say it gets better, it does. It just takes time. The days do get brighter."