As Life & Style previously reported, Selena Gomez's trip to rehab at the end of August wasn't just to treat her lupus and other health issues.

Sources say that the 24-year-old's lingering attachment to ex-boyfriend Justin Bieber is partly to blame for her unraveling this summer.

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"Justin is such poison to Selena," an insider tells Life & Style. "Even when he isn't around, she is still self-destructing because of him."

selena gomez justin bieber getty images

Selena and Justin in 2011.

After fighting with the pop star over Instagram, the brunette beauty vowed not to contact the 22-year-old while receiving treatment, but eventually reached out to him.

"Her addiction to Justin is what everyone is afraid is going to take the ultimate toll," the insider explains. "Justin takes her to a dark place mentally, and she really can't let go."

For more on Selena’s downward spiral, pick up the latest issue of Life & Style, on newsstands now! And scroll through the gallery below to see the former couple in happier times.