"They've been friends since they were kids and have always been there for each other whether they've been close or not," says a source

Selena Gomez and Demi Lovato have had their ups and downs through the years since first becoming friends at just 6 years old, but the stars will always have each other backs no matter what.

“I’m sure she’s very upset,” says a source close to the “Back to You” singer, 26, about Lovato’s apparent overdose on Tuesday. “They’ve been friends since they were kids and have always been there for each other whether they’ve been close or not.”

Lovato, 25, is currently still recovering in a Los Angeles hospital but is “awake and talking,” a source previously told PEOPLE. While TMZ initially reported the overdose was heroin-related, multiple sources close to Lovato claimed to PEOPLE that it was not.

Lovato has battled addiction, mental illness and disordered eating for years. In 2010, she entered treatment, where she was treated for bipolar disorder, bulimia, self-harm and addiction. She relapsed after she left the treatment center, then entered a sober living facility for a year.

Selena Gomez and Demi Lovato

“Demi reached out when Selena had her kidney transplant. They will always care a lot for each other and Selena will be there for her friend,” adds the Gomez source.

Last fall, the former Disney darlings reunited at the InStyle Awards where they hugged on the red carpet and were seen catching up inside.

Lovato gushed about Gomez’s single “Fetish” before her pal returned the social media love a couple months later after watching Lovato’s candid and emotional YouTube documentary Simply Complicated. “This was beautiful,” Gomez commented on Lovato’s Instagram post. “I’m so happy for you. You always continue to be bold and real. I wish more people were like you. Love you.”

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Demi Lovato and Selena Gomez
| Credit: Everett

In March, Lovato revealed she celebrated six years of sobriety, but just three months later released a new song, “Sober,” and revealed that she had relapsed.

“Mama, I’m so sorry I’m not sober anymore / And daddy please forgive me for the drinks spilled on the floor,” she sang on the heartbreaking piano ballad. “And I’m sorry for the fans I lost who watched me fall again / I wanna be a role model, but I’m only human.”

RELATED VIDEO: Demi Lovato Not Under Criminal Investigation After Apparent Overdose: Police

Sources tell PEOPLE that Lovato has been “a total mess for months,” and some point to her new perspective on sobriety and a subsequent split with Mike Bayer, her longtime life coach, as a major red flag.

Demi Lovato
| Credit: MARK RALSTON/AFP/Getty

“Demi began to feel that the belief that total abstinence is the only way to deal with addiction is false,” a source with insider knowledge of the situation told PEOPLE.

“She essentially said that she felt it wasn’t the only way and that she can handle her addictions, and she would rather attempt controlled consumption,” added the insider. “She felt that she could drink in moderation and she believed she wouldn’t return to harder drug use, and that alcohol was never really a problem as much as other things.”

If you or someone you know is in need of help, please contact the SAMHSA substance abuse helpline at 1-800-662-HELP.