Mia St. John lost 30 years of sobriety after her late husband suddenly died on Feb. 3

Kristoff St. John‘s ex-wife Mia St. John is opening up about how the tragic and sudden death of her late ex-husband has impacted her life.

“I lost my 30 years’ sobriety,” the professional boxer, 51, revealed to PEOPLE. “I’m ashamed, believe me. I had 30 years of sobriety, I thought I was the s—. Like I was queen of mental health. I’m a mental health advocate. I felt as small as you can get. My ego was crushed. But I feel like I want to look at the bigger picture and my higher self. It’s about the good of all. And if I can help someone out, and say if there’s just nothing it doesn’t mean that I’m a weak person. I’m just an imperfect person and we all have to find a way to pick ourselves up and carry on.”

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St. John was found dead at a home in Woodland Hills on Feb. 3. Just two weeks earlier, the Young and the Restless star had mourned the loss of his son, who died by suicide four years ago.

Kristoff was last active on Twitter on Jan. 21, when he retweeted someone’s post about losing a child that reads, “Grieving the loss of a child is a process. It begins on the day your child passes, and ends the day the parent joins them.”

“Never a truer word was spoke,” St. John tweeted. “Thanks for posting this.”

Kristoff and Mia’s son Julian died by suicide on Nov. 23, 2014, at the age of 24 following a lifelong battle with mental illness. He was reportedly found unresponsive in the bathroom of a Long Beach, California, facility.

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Mia told PEOPLE that both she and Kristoff “changed drastically” after losing Julian.

“Our son had schizophrenia, both him and Kristoff suffered from addiction,” she said. “It was a very difficult, and a sometimes painful life. Kristoff was always working on himself, and trying to get better. He kind of had like these two separate lives, and not very many people knew about, the darker side. But, that’s what I have been trying to speak out about, because I feel like if we don’t, then the harder it is for anyone to ever get help.”

“I always felt like I was the one that was struggling the most,” she added. “But what I realized later was that wasn’t the case, it was just that I was more vocal about it. And Kristoff held it all inside. So like I said, he would just break down and he would go back to drinking and taking pills and that’s how he dealt with it. I think that is what lead to the downfall.”

Mia said she was speaking to him “as he was dying.”

“He kept saying, ‘I just don’t want to live anymore, I don’t want to live anymore.'” After pleading with him to hold on, Mia knew this was the end.

“All of a sudden he says, ‘One second, one second, Mia, Julian’s at the door. Julian’s here.’ And I started screaming, ‘No!’ Julian wants to see you but not today, this is not the day! And I start to panic. And he said, ‘It’s okay, it’s okay, we’re just going for a walk.” Looking back, at the timeline of when he passed and when the paramedics got there. I believe he was already dying while we were on the phone.”

Credit: Julian St. John/Facebook; Robert Voets/CBS/Getty

Following Kristoff’s death, Mia was hospitalized twice.

She shared the news on social media Saturday, alongside a photo of the late Young & the Restless star posing on the red carpet with his two daughters, Lola (with ex-wife Allana Nadal) and Paris (with Mia).

I’m out of the hospital. I’m sorry if I scared anyone,” she wrote. “Let’s plz focus on the wellness of his precious girls Lols & Paris.”

“They love their father so much, the beautiful, loving, funny soul that he was/is,” she continued, adding a green heart emoji. “#MentalHealth is all we have, nothing else is important.”

Credit: Getty Images

Kristoff was buried next to Julian following an emotional memorial service Monday in Westlake, California. Now, Mia is continuing to speak out about mental health.

“Never be ashamed because every one of us suffers from some mental health issue,” she said. “But I’m going to continue to speak out, even if it hurts my ego. I’m going to speak out and I’m going to continue to let people know about mental health. I’m not going to stop talking about it. I’m going to continue to fight in the honor of my boys that I lost.”

Kristoff is also survived by his fiancée, Kseniya Mikhaleva.