New claims about Selena Gomez's shocking check in to rehab says that it was her ex-boyfriend Justin Bieber's hookup with Miley Cyrus that caused a downward spiral, Hollywood Life reported Thursday.

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An insider said that Gomez confessed during group sessions in rehab that it was Bieber's cheating ways that sent her there.

"She told the group how much she was struggling with Justin's infidelity and his obsession with hooking up with other women. She learned from mutual friends time and again that Justin was cheating, and that knowledge was breaking her heart."

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The source went on to name Bieber's speculated relationship with We Can't Stop singer as a factor that took Gomez down.

"She kept talking about a girl named Miley-- a friend of hers who betrayed her by hooking up with her boyfriend behind her back. Dealing with stories about Justin's random hookups were bad enough, but hearing that he was involved with one of her closest friends was the ultimate betrayal for her."

According to a friend of Gomez, her issue with drugs was totally influenced by Bieber. They said the Boyfriend singer pressured his then girlfriend to try certain things, so she did.

"She finally gave in to pressure and started smoking weed with Justin. His house was the first place she tried it. She doesn't smoke anywhere near as much as Justin, buts he does have a problem, and her parents blame [Justin] for it. They think he's a bad influence."

Gomez allegedly checked in to Dawn at the Meadows in Wickenburg, Ariz. after struggling with alcohol, pot and Rx Ambien. She was slated to stay for six weeks but left early. Her rep maintains "Selena voluntarily spent time at Meadows but not for substance abuse."