Janelle Brown is opening up about the heartbreaking details surrounding her son Garrison’s death.

In an exclusive sit-down with PEOPLE, the Sister Wives star, 55, says that she believes Garrison’s struggles with “substance abuse definitely played a role” before he died by suicide at age 25 in March.

“I think for him, I would say the substance abuse was really probably one of the biggest factors,” says Janelle, noting that Garrison, who she shared with ex Kody Brown, seemed happy and had a lot going in life.

“I don’t know what we could have done different[ly],” she adds.

The TLC star, who will return to TLC screens for season 19 on Sunday, Sept. 15, explains that she and her family members had “real conversations” about his struggles and offered “resources” to help him push past his addiction.

“We were always talking to him, we were loving him. All the things were there,” she reflects. “It really just was something he could not… like the demon he couldn’t get on top of the battle. He couldn’t seem to get over. And it just wasn’t for lack of love or lack of anything.”

Sometimes, Janelle admits she can’t help but think “could we have done something more, but I don’t know.”

“I think that’s a grief trap because I think ultimately everybody is responsible for their own actions and their own decisions,” she continues. “We did everything. We really did everything that we could have done. And unfortunately, sometimes that still isn’t enough.”

She adds, “I think the biggest thing is to remember that, ‘What if I did this, could I have done this?’ That’s a weird mental game we play with ourselves sometimes when we’re in grief.”

On March 5, Garrison was found dead in his home in Arizona. At the time, Lieutenant Charles M. Hernandez II of the Flagstaff Police Department told PEOPLE that officers responded to a report of a death inside a home and confirmed that Garrison’s brother Gabriel, 22, had “discovered Mr. Brown deceased.” Officials later ruled his manner of death as a suicide.

Garrison had been a part of TLC’s Sister Wives since its debut in 2010. In addition to Garrison, the now-exes Janelle and Kody Brown also share daughters Maddie, 28, and Savannah, 19 as well as sons Logan, 29, Hunter, 27, and Gabe.

Shortly after his death, the former pair shared a joint statement addressing the news on their respective Instagram pages.

“Kody and I are deeply saddened to announce the loss of our beautiful boy Robert Garrison Brown,” Janelle wrote in her post. “He was a bright spot in the lives of all who knew him. His loss will leave such a big hole in our lives that it takes our breath away. We ask that you please respect our privacy and join us in honoring his memory.”

Janelle has since paid tribute to her son on multiple occasions, including recently on what would’ve been Garrison’s 26th birthday. “We are missing you terribly today. It’s hard to believe you aren’t here anymore,” she wrote in April. “I still feel you nearby sometimes. And I’m grateful we will see each other again when my journey is completed.”

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Sister Wives season 19 returns Sunday, Sept. 15 at 10 p.m. ET on TLC.

If you or someone you know is considering suicide, please contact the 988 Suicide and Crisis Lifeline by dialing 988, text “STRENGTH” to the Crisis Text Line at 741741 or go to 988lifeline.org.

If you or someone you know is struggling with substance abuse, please contact the SAMHSA helpline at 1-800-662-HELP.